The USA may be a relatively young nation, but it has no shortage of eccentricities that puzzle the foreign visitor. From supersize food to eclectic roadside attractions, we've picked 32 quirks that the rest of the world will never understand. 

Tipping can be a minefield in the States. While most travellers are used to adding 10% to their food bill, in the US, almost anyone who provides you a service will be awaiting a few dollars. Keep some notes handy in your wallet, and expect to tip the porter, the bartender, the taxi driver and the delivery person. In waiting and hospitality jobs in particular, tipping can make up a large proportion of the workers' final wage.

The whopping portion sizes available across the US are baffling to most foreigners. Fast-food giant McDonald’s phased out its “supersize option” (which inspired cult documentary Supersize Me) more than a decade ago – but venues like Las Vegas’s Heart Attack Grill still peddle their mighty helpings and sinful options. Towering burgers and heaping fried goods are on the menu.

In many parts of the world, a “sandwich” is a few slices of ham and cheese slipped between two hunks of flimsy bread – but Americans take their sandwiches seriously. The US Department of Agriculture even has official guidelines on what makes a real sandwich (it should be at least 35% meat, and no more than 50% bread, with condiments and garnish making up the rest). Chow down on a pit beef roll in Baltimore, Maryland or try a classic Philly cheesesteak in Philadelphia, Pennsylvania.

Whether you’re waiting at a bus stop or propped at a bar, chances are a friendly local will strike up conversation – this can feel a little left field if you’re from a more conservative nation. While of course not everybody is interested in talking to strangers, there’s an openness and conviviality that’s uniquely American. It pays to embrace it.

Most visitors to the US will have eaten peanut butter and/or jelly (jam) in some capacity, yet putting them together is a uniquely American affair. The classic PB&J sees two slices of soft white bread laden with equal parts peanut butter and jelly, and sandwiched together. The first reference to this creation was by a woman named Julia David Chandler in a culinary magazine dating back to 1901.

Food and soda servings aren’t the only things that are larger in the States – pretty much everything is built on a bigger scale. The highways are wide, the buildings massive, the shop signs luminous and looming. It’s easy to feel pint-sized in comparison.

While free soda refills are not unheard of in other parts of the world, they’re commonplace across America. Many laid-back restaurants and diners will allow you to top up your cup with as much pop as you’d like, and some places also allow you to guzzle infinite mugs of tea or coffee. The unpractised visitor should exercise caution.

Nearly all states have counties (or equivalent), but these boundaries mean little to the incoming traveller – and they can be confusing when trying to understand the geography of this enormous country. Just remember that these are political or administrative delineations above all else, and you don’t need to get bogged down with the detail.

The sheer babble and bravado can be overwhelming to any overseas traveller who braves a US sports game. Whether it's baseball, basketball, football or hockey, there'll be brash billboards, blaring music and players with no shortage of celebrity swagger. There’s also the prospect of crowd participation, so giant foam fingers are essential to hide behind if that fills you with dread.

The sporting fanfare isn’t limited to the pros though. The level of adoration and interest awarded to US college athletes is puzzling to visitors – school sports games elsewhere usually pass with little attention from outsiders. Many studying sports stars spend hours and hours practising each week, and stadiums are filled with loyal supporters, from the college and beyond.

While nearly everywhere else on Earth has adopted the metric system, most Americans stick to feet and inches. Today, the US takes a hybrid approach (dipping a toe in both systems), and visitors spending any length of time here will need to understand imperial measurements. Time, money and resistance from some of the country’s major businesses has stopped the US from following in the rest of the world’s footsteps.

The legal drinking age in the United States is 21 years old – one of the highest in the world. American bars are also notoriously strict when it comes to checking punters’ ID. Even if you're sure you'll not be asked for proof of age, come prepared so nobody misses out on that sundowner.

The nation’s love affair with artificial air never fails to perplex visitors. Cool air is blasted in shops, theatres, cars and restaurants through the summer, and the heat is whacked up during the winter chill. In fact, the US has historically used more energy on air conditioning than the rest of the world combined. The roots of the obsession is unclear, but visitors should keep abreast of the teeth-chattering temperatures with an extra layer or two.

Fastened on shop fronts, fixed in front yards, draped over monuments – you’ll see the American flag flying proud wherever you go. Most national flags are reserved for official buildings and grand events elsewhere in the world, so America’s patriotic obsession with the stars and stripes takes some getting used to.

There are more than 200,000 fast-food restaurants in the United States – that’s a lot, even for such a large country. The sheer ubiquity of junk-food outlets is matched nowhere else in the world. Though most travellers will be familiar with Colonel Sanders, or those golden arches, they’ll be amazed by the number packed into a single block.

When Americans pen the date, they write the month first, followed by the day, finishing with the year. This can be a confusing detail for the foreign traveller – but it’s one you’ll need to get to grips with quickly, or you’ll risk missing that dinner reservation or broadway show.

If you’re planning some retail therapy during your trip to the US, best practice your mental maths. Tax (which varies from state to state, and can be checked online) is excluded from an item’s price tag and added on when you pay. Try and tot it up before you reach the checkout to avoid any nasty surprises.

America’s all-singing, all-dancing malls put many of the world’s dreary shopping centres to shame – and some can be frankly overwhelming at first visit. Though they’re fewer and further between than they once were, a cavernous shopping mall is still the epitome of the American retail experience, and much more besides. The Mall of America in Bloomington, Minnesota is the flashiest of all, complete with its own theme park, aquarium and, of course, hundreds of shops and restaurants.

Though you're not likely to attend, it’s worth being au fait with one of America’s strangest events: the presidential turkey pardon. In a ceremony with all the appropriate pomp, the serving president “pardons” a turkey to rapturous applause. Thanksgiving follows a few days later. George Bush Senior made the pardoning an official event in 1989 – before this presidents were simply presented with an (unpardoned) turkey. The practice has been baffling foreigners ever since.

America’s obsession with ice puzzles those visitors who prefer their drinks at room temperature. In the past, in Victorian Britain especially, an iced drink was a pleasure enjoyed only by high society – but by the 19th century, it was a commodity America collected and sold to other, warmer countries in need of the stuff. Today, America’s icy infatuation shows no sign of abating and it's highly likely you'll find an ice machine in almost every hotel corridor, as well as in the drinks you're served in a bar. 

If you’re in the USA towards the end of October, the showy Halloween festivities will not go unnoticed. Pumpkins sit plump on every porch, shop windows are bedecked with cobwebs and, on the big night, parades of costumed children take to the streets in pursuit of candy. Travellers not used to such extravagant displays look on in bemusement.

An alien concept to most visitors, “tailgating” is a party held at the trunk (the boot, to the Brits), or “tailgate”, of the car. They’re commonplace in the parking lots of stadiums and arenas, and usually involve beer, barbecues and some booming speakers. If you see a group of Americans huddled in a car park, smoke rising above the roofs, beats on the breeze, this may well be why.

America’s festivals range from the slightly unusual to the downright bizarre. There’s the Roadkill Cook-off in Marlington, West Virginia, the National Hollerin’ Contest in Spivey's Corner, North Carolina. Not forgetting the Humungus Fungus Fest in Crystal Falls, Michigan. Visitors keen to experience America at its quirkiest are truly spoilt for choice.

Enter any shop in the USA and a buoyant shop assistant will immediately be at your arm begging to help. They’ll pop up at regular intervals as you browse, just to check no issues have arisen since you last updated them. Once you arrive at the checkout, a beaming cashier will probe you about your day. You’ll then be sent on your way, clutching a series of items you only bought to avoid disappointing the spirited staff.

Americans have a penchant for building mammoth structures and leaving them by the roadside. Colourful confections include the world’s largest jack-in-the-box in Middletown, Connecticut, life-size dinosaurs in Cabazon, California and Cadillac Ranch, a series of psychedelic upturned cars in Amarillo, Texas.

For those used to disinterested waiting staff and bored bartenders, the relative enthusiasm of American restaurant workers will also come as a shock. After offering gushing recommendations of their favourite dishes, they’ll stop by to check your progress and wait with bated breath as you assure them, through a mouthful of food, that your meal is cooked to perfection. Remember to leave that tip.

In most parts of the world, if you over-order at a restaurant, you’ll look on regretfully as the staff whisks away your half-finished meal. This is madness to most Americans, who wouldn’t think twice about requesting the leftovers in a take-home container. The name "doggy bag" harks back to the 1940s when, during WWII, citizens were encouraged to feed scraps from restaurants to their pets at home.

Visitors can get on board with the Superbowl – the US loves American football as much as Brits love “soccer”. But what’s confusing is the the half-time ads, which often get almost as much hype as the game itself. They’re always glitzy (and costly) displays with plenty of celebrity cameos, put on by some of the world’s biggest brands (think Budweiser, Coca-Cola and Amazon).

In many parts of the nation, public transport is practically non-existent, and the sheer size of the US means most Americans rely on their car to travel long distances. The great American road trip is a both a common movie trope and a fact of life, and the length of time most Americans are comfortable spending in their car may surprise the foreign visitor.

American cars are giants of the road. The nation’s infatuation with huge SUVs is well-documented but little explained – we can only imagine it’s to match those giant highways.

Unlike the motley dimensions of much world currency, all American bills are the same size. This means you might find yourself fumbling at the checkout, trying to offer a dollar note for something that costs 20 bucks. The assorted names (which bear little or no relation to the actual monetary value) are confusing too: nickels (five cents), dimes (10 cents) and quarters (25 cents). Visitors should get acquainted with them before hitting the road.

While most parts of the world can take or leave summer camp, in the USA, it's a rite of passage. Many Americans you meet will look back fondly on their time frolicking in the nation’s backyard as a kid – and as a trend towards adult summer camp takes hold, big kids are able to get in on the fun too.