A bloke wins the lottery and decides to buy himself a Harley Davidson, he goes down to his local bike shop and after purchasing a top of the range bike, the owner of the shop tells him to coat the bike in Vaseline every time it looks like raining. That night he goes and picks his girlfriend up on his new toy and heads over to her parents house for the first time. As they arrive there, she explains to him that whenever they have dinner, don't talk.
"If you talk," she tells him, "you have to do the pots." The man is astounded as he walks into the house as it is a complete mess. Anyway, the family all sit down for dinner not saying a word. The man decides to take advantage of the situation by groping his girlfriend's tits, yet there is not a sound from anyone.
So he decides to shag his bird on the table, and still there is not a word. He then proceeds to do his girlfriend's mum over the table, but still, amazingly, there's not a word from anyone. Just at that moment he notices the rain on the kitchen window and remembers his precious motorbike, so he reaches into his pocket and flops the Vaseline out.
At which point his girlfriend's dad leaps up and shouts, "Okay! Okay! I'll do the fucking pots!"