bum bra n.— «I noticed the denim was pulling across the top of the back of my legs. Dang, I thought, too tight. Then the clerk pointed at the taut fabric and said, “That’s the bum bra.”… It’s a dynamic trio of jean...
anti-fit adj. (of clothing, especially jeans or trousers) not conforming to the shape of the body; baggy, loose. (source: Double-Tongued Dictionary)