LMTT 

Laughing Myself To Tears.
Used when something is so extremely funny that you acctually is laughing yourself to tears, otherwise use LOL or LMAO.

Friend: *tells something extremely funny*
You: LMTT!

LMTT by w00dy December 30, 2004

Lmtto

It is a new variation on the commonly used lmao in msn messaging. It stands for 'Laugh My Tight Toosh Off'. It is often accompanied with the tongue bearing smiley emoticon in an msn conversation and follows a humorous remark.

"Lmtto. That's the funniest thing i've ever heard."

Lmtto by Jim June 18, 2006