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.
IGS by M@77 J@M35 August 25, 2012