When you hit the public restroom, prior to a long engagement (such as a concert, ballgame, or plane ride), to avoid painful need to urinate, many hours into the event
Be right there, playa! Gonna pre-pee before the big meeting, yo!
Primarily for movie goers, the pre-pee is when one goes to the bathroom before getting the movie starts, in order to avoid having to go to the bathroom in the middle of a movie and miss a good part.
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"