screentalker 

Someone who talks shit or big only behind the screen, while in person they'd use common courtesy and be polite. A person who forgets that others on the internet are real people, and says whatever they want to them without any consideration.

Mary is usually pretty polite in person, but she is a hardcore screentalker on Facebook. You wouldn't believe some of the things she says on there.

They were screentalking, saying things like "kill yourself".

Are you screentalking right now, or are you really this awful?

screentalker by cookie_cake August 2, 2018

screentalker 

One who talks, especially loquaciously throughout a movie, a TV program and/or at a computer monitor

The ScreenTalkers in the row behind kept talking through the entire movie about how different it is from the book

screentalker by ScreenTalkerDotOrg September 22, 2016

screenjacker 

A video game player who looks at an opponent's television, monitor, or display to gain information on their whereabouts or game status.

Every time we play Doom, I catch Tim glancing toward my screen. He is such a screenjacker.

screenjacker by Oden Nauticus January 24, 2005