Hey, mister! There's a fly in your pint!
I will admit that this joke partakes of a bit of national "typing," but I have to say that I have personally observed that it is mostly true. Mostly. Assuming of course that flies are served in pints in pubs, which never happens. ;)
What happens when different nationalities get a pint with a fly floating in it at the pub?
The German jumps up and leaves the pub immediately, loudly complaining about the lack of sanitation.
The Brit calls the barman over, points out the fly, and demands that he pull him another pint.
The Yank puts in a finger, gets the fly out, flicks it onto the floor, and drinks the pint.
The Irishman carefully removes the fly, holds him over the pint and shakes him up and down, crying out "Spit it out, you bastard!"