Unfortunate choice of thread title - you are likely to end up with lots of "A Man Walks Into A Bar..." jokes - a lot of which arealready in other threads here.

Another one, the exact wording of which I have forgotten, but is very much like this:

Every work morning, a man walks into an elevator on the ground floor in the morning on his way to work, presses the 10th floor button, gets out there, and walks up 6 more floors. In the evening, he gets into the lift on the 16th floor, presses the ground floor button, where he gets off to go home. Why does he do this every day?