One of the most obnoxious things is getting someone's hair in your face.
For some reason I just thought of this. Standing too close to someone - in this context a girl with long hair - and she just shakes her hair and it gets in your face. It's not something I can tolerate.
I just find hair disgusting. If you're not tying it up you should not be shaking it in a dense crowd. It's too GROSS.
I find most things about most people GROSS to be frank. There is still reason to single it out.