From the internet and the European Summer Campus 2011 :p
This is apparently a true story. It took place just outside of Munich, Germany.
Heisenberg went for a drive and got stopped by a traffic cop. The cop asked, "Do you know how fast you were going?" Heisenberg replied, "No, but I know where I am."
Q: Why are quantum physicists so poor at sex?
A: Because when they find the position, they can't find the momentum, and when they have the momentum, they can't find the position.