I've been to 25 countries, and there are 16 things you'll almost never find outside the US

Cheerleading is almost exclusively an American activity. Thanks to American movies and TV, many people in other countries are aware of cheerleading, but few have actually seen it in person. For now, it's part of what distinguishes sporting events in the US.

First-time visitors to the US are frequently shocked at the massive portion sizes offered in American restaurants.

While their surprise is justified, they may not realize that in the US, it's also very common for customers to take home leftover food in a take-out box. The practice isn't nearly as common in other countries.

Just about every US college student is familiar with the ubiquitous red plastic Solo cup. It's such a staple of American party life that no American-themed party in another country is complete without it.

One pleasant surprise about shopping in a foreign country is that in many places, all taxes are included in the price you see on the sticker. That means you know right away whether you have enough money to pay for something, and you don't have to do any mental math as you approach the cash register.

Surprisingly, mailboxes aren't very common outside of the United States. It's much more common in Europe, for example, to have your mail delivered through mail slots on your front door.

Tipping is common in many countries, but not to the degree that Americans are accustomed. It's especially clear in restaurants — while Americans tip between 15% and 20% for a typical meal, in most other countries the tip never exceeds 10%. There are plenty of countries where tipping is not expected at all.

In many parts of the US, college sports are more like a religion than a hobby. The same fanaticism doesn't translate to other countries. In my experience, there's no country that cares about college sports more than the US, and it would be unheard of for a college sports team to be more popular than a professional team.

There are drive-through liquor stores in about half of the 50 US states, but the idea is practically unheard of in most other countries. Australia seems to be an exception, however.

America is already an outlier for having such a high drinking age — its national limit of 21 is tied for the highest in the world. But what sets the US even further apart is that its restaurants and bars actually enforce the drinking age by checking customers' IDs.

In other countries, even places where the drinking age is 18 or lower, the legal limit isn't necessarily enforced.

Here's another food you simply won't find outside of the US: biscuits. Although to many Americans, they are buttery, crispy, doughy perfection, you'll be met with blank stares if you try to describe them outside of the US.

And good luck trying to find them in the United Kingdom or other Commonwealth countries — over there, a biscuit is another type of food altogether.

America's huge portion sizes aren't confined to just food. In American restaurants, customers are usually entitled to free refills of their soda, tea, or coffee. But in many places around the world, the drink cups aren't bottomless. In some places, like Argentina or Malaysia, you even have to pay for a refill on tap water.

Americans have a reputation for being overly patriotic.

People in the US are probably used to seeing American flags just about every public place they go — schools, office buildings, post offices, churches, and sports stadiums, to name a few. In other countries, even patriotic ones, it simply isn't common to see national flags everywhere.

Advertising for legal services on television may raise a few ethical questions, but it's perfectly normal in the United States. It's one thing non-Americans often find unusual when they visit the States.

On that note, advertisements for prescription drugs are another thing you won't find often outside the United States. But as anyone who's ever watched a football game can attest, they are unavoidable on US airwaves.

America's obsession with guns is often a surprise to people visiting the US. Perhaps nothing exemplifies American gun culture than gun shows, where customers can view and purchase a wide array of firearms. As many as 5,200 gun shows take place across the US every year.