Knock on douchebag's door.
When douchebag answers, come at him like a spider monkey- a deranged, rabid spider monkey.
Punch/kick him right in the nuts.
As he writhes on the floor and cries, "Whhhhyyyy??!?!?!", You point at him and yell very scarily, "YOU KNOW WHY!!"
And he will know why.
Dave (answers door): Oh, hi..
(Sara, crazy eyes and all, punches Dave in the nutsack)
Dave (falling to the floor): WWWWWHYY?
Sara: YOU KNOW WHY!