I used to think after the fact, about all of the intelligent answers I could have used when people were impolite or ignorant to me. I never had a problem being there for someone else though.
Being well brought up. I did not want to have an "enemy". As I matured, I realized that allowing myself to be beaten into the ground was not good for my self worth.
Now, if I feel I have been criticized, I let the person know that I do not appreciate their comment or their behavior. I keep it to the point and do not get all fussed up. Most of the people do act aggressive because no one wants to deal with their temper. Once you deal with them with dignity, but no nonsense, they think a bit more about their behavior.