A GUY WALKS INTO A BAR

An amnesiac walks into a bar and asks the bartender, "Do I come here often?"

Here's a string of jokes that begin with, "A man walks into a bar..." or some variation thereof. Some are funny, some make you groan.
http://notorc.blogspot.com/2007/09/anatomy-of-humor-5-guy-walks-into-bar.html