"Shagging his Mom" joke

Three guys are drinking in a bar when a drunk comes in, staggers up to them, and points at the guy in the middle, shouting, "Your mom is the best piece of ass in town!"

Everyone expects a fight, but the guy ignores him, so the drunk wanders off and bellies up to the bar at the far end.

Ten minutes later, the drunk comes back, points at the same guy, and says, "I just did your mother, and it was sw-e-et!"

Again the guy refuses to take the bait, and the drunk goes back to the far end of the bar.

Ten minutes later, he comes back and announces, "Your mother was squealing the whole time!"

Finally the guy interrupts. "Go home, Dad, you're drunk!"