I generally don't mind when people touch my hair, but then again I've never had someone walk up to me and deliberately grab my hair or make a big deal out of it. Standing in line at the grocery store and feeling a light tug from behind doesn't bother me. I'll either ignore it or turn around and smile at the person.
HOWEVER.
I have this one friend (God bless her, I love her dearly) who has thick, pin-straight hair and doesn't understand curls at all. And she thinks it's hilarious to make me frizzy. So, while almost everyone else has the common sense to gently take a curl between two fingers and "boing" it,
she starts fiddling with the ends and combing her fingers through it! 
And then she wonders why I yell at her. (she has been warned. Multiple times.)
But, I did get my revenge.
She sometimes curl-irons her hair into these big loopy wave-curls, so one day I just went up to her and started raking my fingers through it, and all the curls immediately fell out. She flipped, and I said "Wow, it must suck having someone run their fingers through your hair without permission and ruining your curls!" *pointed look*