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.
by ShamayaXI September 10, 2009
Snickering in Silence
new for LOL because it applies much more than LOL when texting/typing and trying to be quite
While texting in class i received a message with a prime time to say "thats what she said" and/or "reminds me of my saturday night" or even "I get that all the time" so I sis'd vs lol'ing

"idk what happened it just went everywhere after i touched it"
"reminds me of my saturday night"
by kevin "k-bone" December 25, 2009
Due to the vast majority of lies which happens every time a person types 'LOL' in texting or the internet, SIS (Smile in Silence) is a much more proper use in times when one does not actually laugh when typing 'LOL'. Though, this may suggest that the person is not as fun as he did not actually laugh.
A: Yo, B, I just tried walking thru at a drive thru.
B: LOL, what happened?
A: B, stop lying bro, don't tell me you actually laughed at that message. SIS
B: Jeez, such a stickler...So what happened?
A: They told me that they only viewed car owners as acceptable customers.
by Shinigami Prophet July 10, 2014
An acronym for Sudden Insanity Syndrome
Joan Crawford had a lot of experience with S.I.S. moments.
by Candide March 06, 2008
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.
by Ahseetz Mahpants January 16, 2008
Secret Internet Shorty, an acronym used to describe pictures of a guys dick but using angles or photoshop to make appear significantly bigger than it really is.
Look at this dickture I just got from this guy! I know know for a fact he is a SIS!
by IamIwhoIam August 16, 2011
An online term that depects ''Smile-In-Sight'' used when you don't go as far as to laugh, but a smile still spreads upon your face.
Janet: ''Stacy totally spilled Kool-Aid all over her dress!''

Wayne: ''SIS. That makes me smile''
by Kevin H***ley July 10, 2008

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