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1.
nmu
The most pathetic response anyone can give you during a text or instant message conversation.

Mostly used by immature girls that don't actually give a fuck about what you're doing...especially if they couldn't even type out something longer then a 3 letter response.

2nd in pathetic to "lol", people that use "nmu" in a serious form deserve to be forever deprived from their cell phones and computers.

If a response as pathetic as "nmu" is used as a response, you should not even respond in the first place.
Guy: Hey what's up??
Girl: nmu
Guy: Wow that's a fucking pathetic response
Girl: Soorrryyy I'm (insert bullshit excuse here)
by ItstheWaveTV September 22, 2009
 
2.
not much, you
also: nm e - nothing much either
"sup" "nm u" "nm e"
by ben and vin December 29, 2005
 
3.
nmu
Online lingo; abbreviation for "Not much, you?"
-"What's up?"
-"nmu"
by markotsay7 May 24, 2003
 
4.
nmu
The emu's more popular and successful cousin; commonly used in AIM slang.
Person: hey what's up?
Other Person: nmu?

OR, EVEN BETTER...

Person: hey what's up?
Other Person: NMU ATTACK!
by Teh Kt-zors! May 29, 2007