When it comes to sex appeal, curves matter--the curve of the waist, chest, back, and shoulders, and for many of us, the butt. Male or female, the butt is often a source of envy and desire. There are ideal shapes and specific contours that catch the eye. Everyone has their favorite type, and tastes do vary. But nearly always, the butt should jut backward, curving at a specific angle at the top. It should have a smooth, youthful look, and it should be round and pronounced. Nobody wants it to be flat, shapeless, or saggy. Flat butts are not sexy at all. But not everyone is blessed with the kind of booty they’d like to show off.