If that happens in an argument you should take solace in the fact that your avatar is the only fault they can find to pick on and not your ideas.I know, but I feel like everything has a place and a time, and I'll severely lose my arguing strength if I put that on. It would be nothing but cheap shots.
Like when people can't counter your points, and so resort to making fun of your appearance. It says more about their debate skill than about you.