lmbo Share definition Flag before it meant "laughing my butt off" but now the meaning has changed to "laughing my BOOBS off" guy: that was so funny girl: yeah i was lmbo (laughing my boobs off)! lmbo by Plaidtastic January 1, 2009 0 0 Get merch Get the lmbo mug. Buy Now — $32.95 See more merch