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1.
Not Sure If Sarcasm. Used when you're not clever enough to know if someone is being sarcastic or not, but you're modest enough to admit it.
A: omg you're awesome. I love u 4ever <33333
B: nsis
A: ... definitely sarcasm
by vicious vaca April 29, 2011
 
2.
NSI
No Sarcasm Intended
used when you make a smart Alec remark when you dont mean to be a smart ass.
That is so sad. i think i wanna cry.

Hm. Smart Ass.

Chill man, NSI
by haleymadeethisss May 06, 2011
 
3.
Nsi
Naval Science Intructor
MSgt. Borland is my NSI. He knows everything.He is a Marine. He is God.
by CPO November 27, 2003
 
4.
NSI
No Sarcasm Intended;

When you're texting and you say something that isn't meant to be interpreted sarcastically.
Brett: Dude, I got 1st place in the race!
Bruce: Good for you!
Brett: ...
Bruce: NSI
by TextingNSI July 20, 2013
 
5.
Not sure if serious
John: "What's Nsis?"
Bruce: Not sure if serious.
by Not sure if serious June 15, 2014
 
6.
Abbreviation of "Not Sure If Serious"
Mohammed: Cheryl Cole aint even that hot you know
Brandon Nyathi: What? NSIS
by NYATHI09 February 14, 2011
 
7.
Nsi
Damn Brit.
Look at all the pos, especially Nsi.
by Fect February 06, 2003