If it is malicious (esp. against my family/friends), I will react appropriately but rarely physically. If the comment was made with others witnessing, I will try to humilate the person to the point he/she will never even think of passing a sly remark to me. If it is public and I barely known the person, I try to ignore it with no confrontation. This is where I view the comment as a character flaw that is their problem, not mine.