"Laugh To Myself" - because not everything funny warrants a LOL; also, more suitable form of laughter when at work or the school library where 'laughing out loud' is frowned upon; and, let's face it, LOL is played out and just all-around obnoxious.
Friend - "wut up?"
Me - "nothin. bored at work"
Friend - "at least you have a job"
Me - "LTM"
Laughing To Myself. A preferable alternative to the infamous "LOL". This term is to be used in text/email/IM forms when one wishes to express that they find something funny but aren't ACTUALLY laughing out loud.
A-You'll never guess what happened last night!
A-I got hit in the face with pie!
B-LTM! That's crazy!