It only bothers me if they act on it. One time I was sent to the office to get something for a teacher in school and I saw my Home Ec teacher in the hall when I was going down the stairs, she is in her 60's and has always been so grumpy, well I decided to greet her nicely, since I was in a good mood and she just stood and glared at me, but it made me laugh and I tried to continue without causing trouble.
Anyway about an hour later I got called out of another class by my Irish teacher saying that the Home Ec teacher was thinking of pressing charges for intimidation because I was sneering at her.. I know I didn't intimidate her and I lost all respect for her that day, when people act like that, spreading lies about someone when they are supposed to be a professional it really grinds my gears.
There are and have been plenty people who don't like me for no reason but they don't try to vocalise it apart from letting me know and I am fine with that, it doesn't bother me, if they don't like me then they are not worth making an effort for.