Dunno if this has been done b4...

A man walks into a pub and sits down at a table. He notices a leper at the bar. He orders a shot, drinks the shot and then throws up. Next he orders a beer, drinks the beer and then throws up. He does this for several more drinks when finally the leper comes over to his table and asks him, "I'm sorry if my appearance is making you ill." And the man replies, "No, it's not you. It's the man next to you dipping his chips into your neck.