jiggle the doorknob
how friends in college tell each other they are at their room without knocking so to not scare them into thinking it is an RA at the door
Friend 1: hey when you get to my room tonight just jiggle the doorknob so I know it’s you.
Friend 2: why can’t I knock?
Friend 1: because RA’s knock duh
Friend 2: why can’t I knock?
Friend 1: because RA’s knock duh