Justin Bieber -- Dave and Busted ... Allegedly

Justin Bieber is under investigation for allegedly trying to snatch a cell phone from a guy who snapped pics of Biebs and Selena Gomez at a Dave & Buster's.

If Biebs can't keep chill in a freakin' arcade ... it's a bad omen for the next TWO years while he's on probation! Dude's gotta know better.