Ninja brb Share definition Flag When someone "brb"s but doesn't tell the other person, usually on the computer. Guy 1:Hey, did you see that new movie? (Five minutes later) Guy 1: you ninja brb'd on me, didn't you? Ninja brb by Lateon September 3, 2009 0 0 Get merch Get the Ninja brb mug. Buy Now — $32.95 See more merch