LMDAO Share definition Flag Web-speak for "Laughing My Damn Arse Off". Derived from LMFAO, and also used in many of the same contexts as LMAO. "My God, do you live near me? It's a small world! LMDAO!" LMDAO by Kishi Kat December 28, 2005 0 0 Get merch Get the LMDAO mug. Buy Now — $32.95 See more merch