Why do some people give you dirty looks even if you did nothing to them?

Went back to my hometown for a festival with friends and some chick I went to high school with that I never talked to and haven't seen in years gave me the dirtiest look ever. I barely even know her name and don't remember saying a single word to her ever. It was not just a funny look on her face either, it was an unmistakable bitchy glare.

This is not the only time this has happened, though it doesn't happen often. It's almost always another female. 🙄

WTF is the deal with this?