One of my clients is a connoisseur of "A man walks into a bar..." jokes. I made this one up for him, and he thought it was funny enough to share:
A cartoon character named Sam bellies up to the bar and orders a yard of beer.
The barkeep asks him, "Are you sure you want a whole yard now? It'll get warm before you finish."
Sam replies, "Yes, I'm sure. I've got a 2-dimensional gullet, so this beer will disappear in nothing, flat."