How often do people glare at you?

I came to a 4-way stop, with my left turn signal on. Opposite of me was this girl on her cell phone. Anyway, I waited for her. She was there first so she had the right-of-way. While she was ping me she looked at me like I murdered her mother. This is scary because I don't look at people like that unless I mean it (ideally anyway). Part of me wants to give even a dirtier look to retaliate. Another part of me feels retaliation is weak, and anger is a petty emotion. How often do you experience this? How do you deal with it?