What is a respectable way to respond to an insult to your poem?

I have noticed here on yahoo answers, that commenters range from the young and slightly uneducated in poetry to the cynical internet punks who have a sociopathic need to feed off of insulting people's poems. (and I suspect half of these are uneducated in poetry as well, though they put on a good show.) From being in some of the toughest workshops on the internet, such as the poetry free for all, and taking some cles, I have learned that the proper way to accept a critique is to thank the person and move on. And I whole heartedly agree with that sentiment, since a person taking their time to even read your work is something a writer should be greatful for, and any kind of critique is helpful. However, there are people who blatantly abuse this rule, and go around leaving overtly rude and immature comments which are often directly, and personaly insulting, for lack of a better word, on sites and forums such as this. So, what do you think is a proper way to respond to these people?