Laugh Out Loud Quietly To Myself.
some comedian came up with "LQTM", Laughs Quietly To Myself, as a new IM/TXTing abbreviation. i myself, never really LOL, occasionally i LQTM, mostly i LOLQTM, which is a slight giggle.
when talking about someone else, the abbreviation LOLQTH, Laugh Out Loud, Quietly To Himself/Herself, would then be appropriate.
IM person 1: "omg, gtg, brb, my cat is on fire."
IM person 2: "LOLQTM."