The Guinness joke made it to Fark, and the comments thread there is filled with some of the absolute best “a guy walks into a bar . . . ” jokes of all time. It could quite possibly be the finest collection of bar-related humor on the Internet.
Here’s one of my own, that I’m about to add to the list:

A guy sits alone at a bar, drinking his beer. From out of nowhere, he hears a voice say, “You look great, man! Have you lost weight?” He looks around, and confirms that the only other person in the bar is the bartender, who is all the way at the other end of the bar. He shrugs it off, and takes another drink of his beer.
“That’s a really nice suit. It looks good on you,” the voice says again.
The guy looks around, and before he can say anything, the voice says, “You have very nice eyes.”
The guy freaks out, and shouts, “Hey, bartender! Come here!”
As the bartender arrives, the voice speaks again. “That’s a nice haircut!”
“Who keeps talking to me?!” The guy asks the bartender.
“Oh, that?” The bartender says, “It’s the peanuts. They’re complimentary.”

Thank you, folks. Try the fish.