It's a concept sweeping youtube in which a person draws eyes on their chin, covers the rest of their face (and shoulders, if they're in the frame) lies upsidedown, and then proceeds to film themselves lip-syncing to a song.

Some videos of this fad are:
youtube.com/watch?v=BUfmD6kgljk
youtube.com/watch?v=8j_z8vepBrA

A casual invitation / threat used by an individual that is not afraid of fucking someone up.

A hilarious internet phenomenon where you draw on the basic features of a face on your chin, lie upside down, and record yourself miming a song with the camera zoomed up on your mouth. It should look like a weird, Jabba the hut-esque creature with giant lips singing.