Three guys are drinking in a bar when a drunk comes in, staggers up to them, and points to the guy in the middle, shouting, "Your Mom's the best lay in town!" Everyone expects a fight but the guy ignores him and the drunk wanders up to the end of the bar.
Ten minutes later, the drunk comes back, points to the same guy, and says, "I just screwed your mom and it was really sw-e-et!" Again the guy refuses to take the bait, and the drunk wanders off.
Ten minutes later, he comes back and announces, "Your mom even let me...."
Finally the guy interrupts, "Go home, Dad---you're drunk again!"