I do find a lot of humour differences between me and my American buddies...
Whenever I'm being properly funny, it's very subtle and usually depends entirely on the context of what I say than anything else.
Whenever I swear, I seem to breach all the US laws of decency and insult them quite seriously, yet by contrast, whenever they swear it is crass, childish and base beyond belief, without any art or refinement. We cross each others' lines so easily that I just tell them to always assume I'm making jokes.
I did rather enjoy explaining to them the subtle differences between a shit, prick, nob, wanker, tosser, arsehole and complete c**t, and when each is best applied.