AIO for feeling uncomfortable with my bf’s sister pulling my chin fat?

I’ve (26F) been with my bf (26 M) for a couple years now and I’ve always felt uncomfortable around his family. I am Hispanic and he is Vietnamese and 2 years ago, his sister told him how she doesn’t like me because I’m not Vietnamese and has always been fake nice to me (confirming my suspicions that they were always fake towards me). She never said anything to me and tried to act like she loves me or something.

I do have body dysmorphia and have told my bf that I don’t like having my chin fat pulled since it triggered my BDD. Yesterday we went over to their house and I was sitting next to my bf on the couch and she sat next to me, kinda pushing me out of the way and turned her back completely towards me to talk to my bf and I had to get up and move to the other side of the living room. My bf then for mad at me because I wasn’t sitting next to him so he refused to translate what his sister was telling him (she is fluent in English but only speaks Vietnamese around me).

After, my bf got up and she got up and came towards me and just pulled my chin fat and laughed at me. I told my bf and he said how I’m overreacting and it’s just a sign of “endearment” he said how he will not say anything because he didn’t even see it.

I feel like I’m overreacting in all of this but I do feel uncomfortable with having my chin fat pulled like that. Idk, the other times I’ve seen her doing that to my bf, is to make fun of him for being “fat.”

AIO for feeling uncomfortable with having my chin fat pulled?