I knew the punchline for this one as soon as I read the first line-- because the first time I saw this joke I couldn't stop myself from laughing hysterically fo

I knew the punchline for this one as soon as I read the first line-- because the first time I saw this joke I couldn't stop myself from laughing hysterically for ages. I tried telling it to my girlfriend to explain just what the hell was so funny, but I couldn't get more than a few lines out at a time before thinking about the ending and cracking up again.