LMOA is a common misspelling of the slang term LMAO which stands for "Laugh My Ass Off." Though LMOA started off as a misspelling of LMAO, some online chat users started using as a replacement for LMAO. Some people have speculated LMOA also stands for "Laughing My Obese Ass."
"Sending the funny pic right now." -Funny Dude
"Got it, OMG LMOA" - Random Chick