XXX- Voted best joke of 2006 in UK

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 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!"