Most people can't tell the British apart from the Americans, but there are a number of subtle ways to see the difference. It's more than just "the Americans have 'Bandstand', the British have 'Top of the Pops'" or "they have Prime Ministers, we have Presidents". It runs much deeper than this!
1) For one, British humor involves a dry response to an otherwise outrageous situation. Picture an alien attack on Parliament, where the Chancellor of the Exchequer (bear with me, those are British words that mean something over there) gets zapped into a giant ball of strawberry jam. A British person would reach the height of humor by saying "pity this happens just when I run out of biscuits." An American would walk over, slip onto the jelly, make a giant mess, and say "I think I landed on his crotch."
2) The British also have a great deal of patience compared to Americans. Their cricket games can last days, and of course it took them hundreds of years to establish free elections. Americans, by contrast, can call the results of an election before the polls are closed and with only 2% of precincts reporting. We also invented pop tarts, for those who found the process of toasting bread to be far too time consuming.
3) Whle the British get credit for subtlety, the same is not true for their sweets! I just wanted to complain about how ridiculously sweet their chocolate is.
4) The British got rid of the Beckhams. It'd only be fair if we could send them Kanye West in return. Maybe they could figure out what to do with him.
5) The British are far more trusting than Americans. They don't even have a written constitution--they just count on the Royal Fambly to not usurp power and start beheading members of Parliament. In America you can be sure that the President would do that in ten minutes if he didn't have that damn scrap of parchment to prevent him from doing so.
6) The British celebrate Guy Fawkes Day, glossing over the poor treatment of Catholics at that time in history. The Americans celebrate Thanksgiving, which is based on a time in American history that we didn't do anything wrong to anybody. Ever.
7) The British have a charming highland folk, who talk in distinct accents and value their autonomy and eat food boiled in a sheep's intestine. The Americans have Arkansas.