I remember when i was growing up we had many slang methods of describing things using the opposite terms. It wasn't always as simple as saying "bad" for something "good," but it seemed to be an expansion and variation on that.
Here are some examples:
"My mom made a cake for my birthday, and it was so crappy"
"Man, this test is great."
"Did you see her win the 50 yard dash? she's slow."
Is there a word for this?