Similar to the "freshman 20". It is when a girl who was really hot goes off to college and when she comes home for summer break you immediately notice that her ass has completely exploded. Eating dorm food every day made her gain a ton of weight. On top of that, all the dorm parties, guzzling beer and late night snacks can only lead to one thing...a huge ass...Dorm Ass!
Zack: " hey Mitch did you see Ashley's since she came home from school?"
Mitch: "Yeah dude, she has a major case of Dorm Ass. It is huge!"