LMCO Share definition Flag An acronym that stands for, "Laughing my cats off." Originating from the geeky MacRumors forums where a member laughed so hard, his/her cats were scared off the bed. "Dude, I heard that Apple's gonna release a PowerBook G5 next Tuesday!" "LMCO" LMCO by joe_schmo December 13, 2008 0 0 Get merch Get the LMCO mug. Buy Now — $32.95 See more merch