If you see someone who has a body part about which you know they are self conscious, it is not in anyone's best interest to draw attention to this body part in a way that is less than flattering. Example? "Damn, girl, you got booty!" is somewhat complimentary. "You really do have a big butt!" is not.
'The more you know...' *swoosh*
P.S. I'm not really that offended. I can make fun of my butt. I can let other people tease me about it. Not everyone is as cool as me ;)