Sorry to dissapoint you there buddy, but women don't have assymetric boobs either.
Most doctors would argue that the vast majority are uneven, although being two completely different cup sizes is more rare. Usually large asymmetry is a sign of breast cancer risk. Basically a 10-15% variation between breasts is completely normal, and is considered the norm not an exception. If you know a girl has ever said her bra was "riding to one side" that means one is larger than the other. Then again girls talk to me that way because I'm gay :\
Silly man, don't talk about what you don't know. Or at least google it first.