When an erect boy and horny girl happen to be on a trampoline. The erect boy lands sitting down and the girl happens to land on his penis. The force from them bouncing smashes the penis up the girl.
(the only safe way to have sex with your best friends hot sister)
Me: Bezzie dave m8, me n ur sis last neet.
Bezzie dave: Omg you cock sucker, did you shagg her? *angry face*
Me: calm down soin, me n her woz on ur trampoline, n i accidently reboundpounded her!
Bezzie Dave: oh, m8, no probz, fancy a spliff on a wonnie?