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1.
IGS
Irish Guy Syndrome
Joe blames everything on someone else--he suffers from IGS.
by Ann_Hedonia October 09, 2008
 
2.
IGS
It stands for inter-gender sleepover. It is a sleepover with both guys and girls, usually consisting of 2 guys and their girlfriends. It is usually one of the best events with the opposite gender in the world of people age 15-18, and almost always leads to sex, or at least other intimate contact.
My friend told me about an IGS he once had, and it sounds amazing. If I ever make the insane decision of possibly ever getting a girlfriend at some point in the next 2 years, I am gonna call a friend and his gf to come over and have it.
by M@77 J@M35 April 02, 2012
 
3.
IGS
Immature Gym Syndrome.

When someone claims they know how to body build, when it is clear they do not.

When said person posts comments on social networking sites about anything to do with their training.
When someone makes baseless, uneducated comments on the effectiveness of a supplement or training method.
Guy 1: "Yea, just eat whatever you want and drink a protein shake and you'll get big."
Guy 2: "You don't need to plan your meals, as long as you use supplements."
Guy 3: "Typical case of IGS."

On Facebook- usually a small guy: "Just had the best gym session."
Everyone else: "IGS"
by IGS Stan February 19, 2012
 
4.
IgS
acronym for "I've got Skills". on xbox live, it is utilized as a warning, to prevent the opposition from experiencing an intensely severe case of pwn'd. so to say, IgS, can be converted to LTGI, or "leave the game immediately", as a butt-whooping, is as inevitable and sure to happen as the the rising of the sun each dawn. members of this clan abide by a strict code of honor, gaming, pwnage, and integrity.
A: 'IgS1337SharP' *headshot* 'everybody else'.
B: 'IgSDeathDealer' *teabag* 'everybody else'.
by Larry V III December 11, 2007