to bend over and
bare the rump to someone as a sick
joke. Also,as a noun,a bared rump exposed as a sick
joke.
"A jacket is better than an overcoat,because you can moon
people with your coat on, that way!" said
Kenny,Kevin,Uriah,Harun,Jamie,Matt,Robert,Bill,Jim,and
Tom,as they pulled down their pants and exposed their moons.
"Oh,come on! We're not mooning you,we're only showing you where poo comes from,little kid!" exclaimed David,Greg,and Mel,as they pulled down their pants and exposed their moons to the little kid. They really were mooning the child.