I'm usually cautious about using words like stupid, ugly, greedy, foolish or retarded about other people, no matter how deserving they may be of such labels. If I really do need to criticise a person, I try to find somewhat objective ways of doing so. Objective as in describing their behaviour and hoping that the problem with it will be self-evident to my audience. When I do want to be subjective, I throw in phrases like "I personally think" and "It seems that".