an extension of the word ROFL. Typically used either to emphasize how much someone ROFL'd or in a cheesy satirical way making fun of people who use such retarded words.
Dude: So I'm at this party and Jason was wasted and he fell through the bathroom door with his pants down!
Guy: ROFL!!
Dude: Then, to make it worse, he shit his pants on the way home in Rachel's car!
Guy: ROFLGANGER!
Dude: Guy, you are so retarded. Why do I talk to you?
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.