lbtmn 

A shortened version of the not-so-popular way of indicating you are laughing in various text programs, laughing breaths through my nose. This is when you aren't laughing out loud due to tiredness, sickness, not liking the person, or just because the joke wasn't that funny and all you could do was change the pattern of your nose breathing.

The genius of it is that absolutely no one will know what it is unless you tell them. If they ever ask, just respond with a cool "idk" or "nvm" to divert from a colossal mess.

Joe (whom you hate): I didn't get into Yale.
You: lbtmn.

Karen: Cindy! How do you catch a squirrel?
Cindy: I don't know Karen.
Karen: GO UP IN A TREE AND ACT LIKE A NUT!
Cindy: lbtmn.
Karen: What?
Cindy: nvm.

lbtmn by Maple Ass March 7, 2009

LTMN 

LTMN - An acronym standing for Laughing through my nose. LTMN is the point just before LOL. It is commonly heard in libraries and work places when people see something funny but it would be inappropriate to laugh out loud.

I didn't laugh but had one of those nose exhalations LTMN.

Dude that was funny picture LTMN.

LTMN by heyguysimisaac March 6, 2013

lbtm 

Laughing Behind The Monitor.

When someone says something funny on irc/im or in an email and you end up laughing behind your monitor screen whilst trying to hide it from colleagues in the office..

Person 1: that's such a funny thing isn't it?
Person 2: /me lbtms
Person 3: oh you bastard, im lbtming now!

lbtm by lbtmer January 25, 2011