A screwboy is a prison inmate who tends to take the side of the "screws" (i.e. prison officers). A screwboy is a prisoner who has been known to:
a) "grass up" another inmate;
b) "suck up" to the prison officers;
c) spend a disproportionate amount of time talking to, socialising with, and generally being in the company of prison officers.
Prisoner #1: "I'm gonna tell the screws about {blah blah blah}..."
Prisoner #2: "Don't be a screwboy."
Prisoner #1: "Why are you always laughing and joking with the screws?"
Prisoner #2: "What, are you accusing me of being some kind of screwboy?"
Geez, did you see the wicked screwboo on her knees? I don't think I'd wear shorts after getting a carpet burn like that. Next time she has sex on the carpet, she needs to wear knee pads!
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.