When a chicks' is so fat, she gets on top of her man to ride him, and due to her weight she leaves bruises. Also a girl who has a lot of fat hanging over her pants and always is angry and your really not sure if she is a guy or a girl.
Holy shit Jason, did you see Tonys' girlfriend? Yeah, he told me when she rides him he gets bruises because she is so fat! Yeah, she's a real Muffin Bruiser!