Here are my favorites.
Crowded elevators smell different to midgets.
When tempted to fight fire with fire, remember that the Fire Department usually uses water.
I got in a fight one time with a really big guy, and he said, "I'm going to mop the floor with your face." I said, "You'll be sorry." He said, "Oh, yeah? Why?" I said, "Well, you won't be able to get into the corners very well."
There are a bunch more that are pretty good.