LMFSO Share definition Flag It stands for Laughing my fucking socks off. Or also a commonly made mistake when trying to type LMFAO. :D 1 Person: ~tells a funny story~ 2 Person: Hahaha I'm LMFSO now. 3 Person: ROFL LMFSO by iAcidic April 4, 2009 0 0 Get merch Get the LMFSO mug. Buy Now — $32.95 See more merch