This is a gay event that nerds and wannabees go crazy about. Very cockypeople and fagit bitches carry pride for this event. The event is found in forensics, or debate.
GSN is short for Gay Sex Now. derived from a common expression - "gay!" but with "sex" added to express the extreme feelings. "now" is to show the importance of how 'gay' it is currently.
"wtf gsn!"
friend 1: damn we gotta go back to school
friend 2: are you serious?
friend 1: yeah i am
friend 2: what the hell?! gay sex now!