How do you deal with judgemental people?

This post was originally going to be a rant, but I figured asking for advice is better. As a 30 year old, I look 15. I will spare you the numerous statements women have made to me when they see me with my children.

One that sticks out to me was, "Eww, wheres the father?" Assuming that since I look young for a mother, my kids must therefore not have a father.

How do you deal with the asses of the world that have the audacity to say to your face what they think about you, your parenting style, your looks, etc.. all while being offensive?

Anything clever? Anything that will gracefully embarrass them back?