s.i.s. 

An acronym for Sudden Insanity Syndrome

Joan Crawford had a lot of experience with S.I.S. moments.

s.i.s. by Candide March 6, 2008

S.i.S. 

Shit is Situational.
(forum speak)

Person A: (When z1,) X > Y.
Person B: But when z2, Y > X!
Person C: *facepalm*C'mon guys, S.i.S.

S.i.S. by ShamayaXI September 12, 2009

S.I.S. 

Self-inflicted stupidity. An injury that you caused to yourself by an act of stupidity.

Friend 1: How did you get that cut?

Friend 2: I was running with scissors down the stairs and my shoes were untied.

Freidn 1: Thats some serious S.I.S.

S.I.S. by Ahseetz Mahpants January 10, 2009

S.I.S 

S.I.S is an acronym for Special Investigation Section.

It is an Los Angeles Police Department's elite tactical detective squad with a straightforward mandate: Track down the City’s most dangerous offenders and take them off the street. S.I.S. are possibly the hardest-working, most dedicated men and women Detectives to wear a badge.

Alonzo: Hey, Mark, where are you transferring to?
Mark: S.I.S.
Alonzo: Yeah, S.I.S. Detective.
(from 'Training Day')

S.I.S by KainJynez June 22, 2009

s.i.s 

Means to "sit in silence" insetad of lol. Usually used if somebody sais something retarded online, its a good way to be honest. Lets face it very few actually laugh at stuff online.

xXihateyouxX: i was like "duhhhhhhh" haha
ay u guys 2003: s.i.s

s.i.s by mat a April 24, 2005

s.i.s 

suprisingly improved sequel
a movie is an s.i.s if

a) the original was brilliant,yet the sequel was better
b) the original was average and no one expected an improvment
c) the original was pure garbage and no one wanted a sequel. a monkey could make a better sequel but this sequel was actually really good

aliens and terminator 2 are s.i.s type a imo

mad max 2 is awesome, it is an s.i.s type b because the first one was quite boring

mate, the star wars prequels were such utter shyte, im glad revenge of the sith was better, it was a type c s.i.s

s.i.s by evan4401 October 2, 2010

S.I.S 

Self inflicted shanks:
Stab wounds that one purposely makes usually to frame someone.

Dude 1: dude he shanked me!
Nigga 1: Naa dats just an S.I.S
dude 2: he was with me he coudlnt have done it
-dude 1 walks off angry-

S.I.S by Brawlar December 18, 2008