I can't believe that your grandmother actually said that about your hair! I wouldn't pay any attention to it though, as others have said it's just her own insecurity talking. (easier said than done though.)
No one in my family has ever made fun of my hair, in fact my mother has always told me that I have beautiful hair...but was always sure to add a negative comment about her own hair. For me it was more the fact that she hated her hair and never learnt to take care of it that effected me. It was the same with make-up, clothing and a whole bunch of things. I basically had to learn how to be a woman myself and always felt a little bit shy even trying! lol!
As for other people making fun of your hair, I have definately had that. It was called a "rat's nest" when I was 11-15 and other variations of the overall "rat" theme (lol! Kind of ridiculous when I think about it now because rats don't even have poofy hair!) But then again I have always prided myself on not changing the parts of me that others hated. (my teeth, my pale white skin and my big ears come to mind.) I will never fake bake, never whiten my teeth (which btw are not yellow but just a natural colour! lol!) or pin my ears back! I'm glad that i'm finally discovering a way to keep my natural hair as well!
I live in Italy now and all of those people who think that having blonde pin straight hair and fake breasts is the ideal are absolutely wrong. The women here are amazing. Young, old, curly, straight, thin or curvy these women accept their bodies and do everything that they can to get the most out of them. Interestingly enough they are regarded as among the most beautiful in the world! I think that all North American women can learn something from them and stop this obsession with trying to look like barbie blow up dolls! (sorry to all those women who look like Barbie blow up dolls naturally! LOL!)