Down south in your mouth
(only for guys) when you stick your hand down the back of your pants, then rub your ballsack. touch the victim or- slap- them in the mouth or face. Then yell "DOWN SOUTH IN YOUR MOUTH!!" no teacher will know what it means.
Colin: oh my god!
Matt:what?
Colin: That ass-hole just did a down south in your mouth to me.
Matt: oh. HA!