They pick on you cause they get a rise out of you. If you literally do or say nothing and just carry on like nothing is going on one of two things will happen.

1. They get bored and move on.

2. Bystanders will be your voice and state how pathetic they are acting by bugging you constantly.

Now in a IRL situation...doing nothing does exactly nothing. Punch them in their smug face. It'll stop quick enough.