I (21F, east asian) was sitting on the train on my way home, diagonally across three younger (non-asian) girls (early to mid teens). I was sitting next to the exiting doors and one of them was standing in front of me when they got up to get off at their stop. She bumps my knee with hers. Does it again- now I know it's intentional. I move my knee to the side and she starts touching and rubbing my hair while saying in a "sweet", patronizing voice "Aww I'm sorry...I'm sorry", and then getting off of the train when the doors opened. I wasn't sure what to do because I was in a physically vulnerable position and I was worried the three of them might physically harm me if I tried anything, so I just lightly laughed and said "please don't do that" while not doing anything else about it!! I felt weak and so disrespected. When I got on my bus I couldn't stop bawling my eyes out. Now I feel angry, at myself and her, that I didn't speak up more assertively and move her hand away from me.

Edit: Thank you all for the support and sympathy, I really appreciate it and it's made me feel better about the situation!