I couldn't think of any American jokes about Americans - we need some! There are plenty of jokes about specific areas of America. I searched for some jokes about Americans but most of the ones I found were probably derived in another country. They were really funny though. I liked this one:
An American was telling one of his favorite jokes to a group of friends. "Hell is a place where the cooks are British, the waiters are French, the policemen are Germans, and the trains are run by Italians."
The lone European in the group pondered all this for a second and responded, "I can't say about the police and the trains, but you're probably right about going out to eat. A restaurant in Hell would be one where the cooks are British and the waiters are French - and the customers are all Americans."