When you drink like you're in a fraternity yet you're not because you're either too old or no longer/not in college
Dude, we got so fratnasty at last night's party. I took down a beer bong and shot gunned beers all night.
by Almarock April 01, 2013
1 more definition
Dirty, deplorable, disgusting condition; the lack of cleanliness and overabundance of filth often found in a college fraternity house.
"When I saw how much old mac & cheese and other greasy funk was matted on that frat-nasty oven, I literally gagged."
by juleskills October 27, 2010