A very loud, unattractive, hard-faced woman walks into Tescos with her two kids in tow, screaming obscenities at them all the way through the entrance. The door greeter says:
"Good morning and welcome to Tesco, nice children you've got there. Are they twins?"
The fat ugly woman stops screaming long enough to snarl:
"Of course they bloody aren't! The oldest is nine and the youngest is seven. Why the hell would you think they're twins?..... Do you really think they look alike, you dickhead?"
"Absolutely not" replies the greeter, "I just can't believe anyone would shag you twice."