A very loud, unattractive, hard-faced woman walks into Tesco 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, he's nine and the younger one, she's seven. Why the hell would you think they're twins?..... Do you really think they look alike, ya di_ckhead?"
"Absolutely not," replies the greeter, "I just can't believe anyone would f*ck you twice!"