OK, here goes.
This guy goes down to his neighborhood bar one afternoon to have a few beers and watch the Cubs game. He's sitting there enjoying himself, drinking beer and eating peanuts and watching the game. Unnoticed by him, these two siamese twin sisters come in and sit down at a table back in a dark corner of the bar. After awhile, the sisters move up to bar and have a seat next to him. One of the sisters, the talkitive one, says "hey, would you like to buy us a drink?" This guy, being a good sport, says "sure" and they get to drinking and talking together. This goes on for quite awhile, and they're all having a good time. Suddenly, the one siamese twin sister says to the guy "Hey, have you ever made it with siamese twins before?" This guy is quite taken aback, and he stutters and stammers around, and finally manages to talk her into just having another drink and talking some more. A little while later, she insists "c'mon, you look like a fun guy, let's go back to our place and party." The guy, still reluctant, has had enough to drink, and thinking to himself "what the hell, I was born to have adventure," agrees. So they leave the bar and head over to the sisters' place. Once they get there, he is getting to feel apprehensive again, so they sit around and have a few nightcaps. Finally, the one sister says "c'mon, let's go into the bedroom." He's had enough to drink by now, and figures "what have I got to lose?" Once they get in the bedroom, they all start stripping down, when the first siamese twin, who has initiated all this says "Look, I don't want you to be shocked or surprised or anything, so I have to warn you that when I am making love, I have a tendency to pass a lot of gas." The guy is like "you've got to be kidding me" but thinks "well, in for a dime, in for a dollar, let's go for it." As the siamese twins get on the bed, the first one says "oh, there is one other thing, while I am being made love to, my sister likes to play the tuba." This guy is totally freaked by now, but there is no turning back. He gets in bed, and they go at it all night long. He's banging one sister, and she's farting like crazy "phtt, phtt, phtt." In the meantime, the other sister is lustily playing the tuba, "oom pah pah, oom pah pah, oom pah pah, oom pah pah." This goes on all night. About daylight, he drags himself out of bed and staggers home to sleep off this drunken escapade
A couple weeks later, he decides to go back down to the bar to have a few beers and watch the baseball game. Unbeknownst to him, the two siamese twin sisters are sitting in the same dark corner. One sister notices the guy, and says to her sister "Hey, isn't that the guy we picked up and took home a couple weeks ago?
The other sister takes a long look at the guy and says, "Yeah, I think it is. Do you think he'll remember us?" (Cue rimshot and Johnny Carson theme song.)