Without using profanity, what is the most offensive generalization that someone can make about you?

The very nature of Q&A seems to breed a lot of generalizations about religion, races, cultures and lifestyles. Most of us will never really know anyone personally that we are exchanging ideas with, so why do some even bother with rude, uninformative or just plain ignorant remarks? I am trying to be a good girl and just answer questions that I feel I have a positive contribution to make, but sometimes a question is just too stupid to take a p. Then I can be a very bad girl, and I don't like that about myself.