You're texting your friend and they happen to say something funny. So you try to type "LMAO" really fast but instead, you type "LMA9". It is annoying as fuck that you just sent "LMA9" but you have to deal with your shame.
A combination of L.M.A.O. = Laugh my ass off And 0wned
if this was put into "english" so to speak, it would be "hahaha you got 0wned"
or "hahahahaa your'e so stupid"