Courtesy of Alicia:
Werner Heisenberg is in his car on the way to deliver a lecture and, being that he is late, is speeding. Inevitably, he zips past a policeman, who pulls him over. Walking up to the car, the officer knocks on the window and Heisenberg rolls it down. "Do you know how fast you were going?" demands the policeman. "No," says Heisenberg, "But I do know where I am."