1. A miss-spelling of "party"
2. A type of extreme party, where one gets drunk, has sex with someone (not necessarily of the opposite sex) and wakes up sometime between afternoon and evening on the roof of someone's house, on their couch, our in their chimney (if they have one).
3. A type of party where only one person becomes the star, usually as an act of crashing said party. Though the second one has crash the party, it immediately becomes a parptay, even if the guests there don't start thinking of him as a star.
Teacher: Mr. Wild, how do you spell "party"?
Mr. Wild: P-A-R-P-T-A-Y, right?
Dude 1: Woah man... last night I had the most extreme parptay ever!
Dude 2: What makes you think that?
Dude 1: All I remember is getting REALLY drunk, having sex with some guy... or girl, then waking up at 3 o' clock in the afternoon on some guy's house.
Dude 2: Woah, that is a parptay!
Bro 1: Dude, I'm gonna rush in that place, and totally crash that parptay!
Bro 2: What?
Bro 1: When I rush in, everybody's gonna go wild for me because of all this beer I'm carrying, and it's gonna turn into a total parptay!
Bro 2: AWESOME! *high five*