Sorry that you were faced with such ignorance. The strange thing is when people speak like that they tend to embarrass themselves in public, and it becomes part of their maturation away from such stupidity. When we totally shut people up, even with their harmful words, then the ignorance festers into something so much more dangerous.
When someone tries yo get into your head like that, you can always return the favor with an intelligent quote, and send him back into the box of duh. The worst thing you can do is get into an argument of four letter words that merits the phrase stupid is as stupid does.