When you are missing your bro or homeboy. So you master-bate to their image or think about them.
Bro:1 I miss bro 3
Bro:2 ya I miss him too that's why I was totally brosterbating to him last night
Bro:1 I wonder if he's brosterbating to us right now Bro:2 I hope so
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.