I just stumbled across this on a German site, nearly fell off my chair laughing at the first one I read.
How do you make a bassist? You take a bit of straw, some beer, and some manure, but not too much manure, otherwise you make a guitarist.
How many bass players does it take to change a light bulb? Five. One to hold the bulb, four to drink beer until the ceiling spins.
Who sits in the test room with an IQ of 50? Two bassists.