Britain
A country with people who generally hate America because they lost the Revolutionary War to them. People from Britain usually have a large sense of national pride, and do not take any stereotypes sitting down. Unlike many other countries, people from Britain can get easily offended by stereotypes, even if they are said jokingly. The British usually like to use random examples like the SAS to show that they are better than Americans (In the case of the SAS, anyone with an ounce of intelligence can look up failed SAS operations on Wikipedia).
American: "Hey, you're from Britain, right?"

Brit: "What, you're gonna call my teeth ugly? Fat cowboy!"

American: "Whoa, calm down man! I'm just acknowledging your nationality!"
Brit: "Oh, go stuff a cheeseburger in your mouth! Anyway, we British are much more technologically advanced than you Yanks! We invented football (which you idiots call soccer) and cricket!

American: "So you're saying that a country that invented the light bulb, Microsoft, Apple, Facebook, the transistor, and 3-D printing is not as advanced as a country that invented some sports?"

Brit: "Too right, mate. Actually, you're not my mate! You're a cunt! Also, we have the SAS!"

American: "Are you in the SAS?"

Brit: "No, so?"

American: "Well, I have three responses for you: 1. The SAS has failed operations, 2. There is no one "best" special operations force, and real members of the SAS hate seeing self proclaimed commandos like your self decide who is best, and 3. You're using the accomplishments of men you don't even know and will never associate as you aren't and probably won't be in the SAS for your own gain? That's pathetic. It shows that you have insecurity that you have to rely on other's achievements to show that you are superior."

Brit: "Uh....I have to go to tea......"

(Runs away, masturbates to picture of the Queen).