Johnny and his friends were drinking in a bar when a drunk comes in, walks up to them and points at Johnny while shouting: "Your Mum is the best on bed in the whole town."
Everyone expects a fight, but Johnny 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 Johnny again saying: “I just did your Mum, and it was so sweet.
Again Johnny refuses to offer a word and the drunk goes back to the far end of the bar.
Ten minutes again, he comes back shouting:"Your Mum liked it"
Finally Johnny interrupts saying: "Go home Dad, you're drunk!