A sweater a woman ties around her waist to hide her ass while jogging, walking or exercising. While most of these women have good figures from their exercise, they are likely self-conscious of others staring at their ass.
"Wow--check out the tight body on that jogger!"
"Yeah...it's too bad she's wearing an ass sweater."
(n.) A grossly or overly hairy ass; an ass that is completely covered with hair, thus covering any skin and only showing the thick mat of hair grown on top; a hairy ass which causes excess sweating
1. John: Dude, is your ass hairy?
George: Are you kidding me? I have an ass sweater!
2. Paul: It's fucking hot out!
George: Yeah, and it doesn't help that I'm wearing an ass sweater!