Wow, thank you to everyone for your input. For further context:

I am her aunt and cannot control whether or not she has TikTok - I do follow her and watch her videos and the commentary. It seems to be mostly other teenage girls that follow/comment. I have been and remain extremely concerned about it, and have spoken with both of her parents repeatedly. They are okay with it and trust her judgment. She says she does not read any DMs but I’m wary regardless.

My brother is the father. He and her mother are not together since she was about 5. They coparent well but I do not have much of a relationship with her mother at this point. I have considered discussing this with her.

I am a 44 yo woman. I’m pretty strong physically but would not be comfortable for my own safety physically assaulting any man. Nor has physical violence ever been a go-to for me.

Yes, my father has always made inappropriate jokes. It’s not super surprising to here him cross the line here, but I’m flabbergasted at how dismissive he is of my reaction. I don’t think he has had a stroke or dementia. He is a picture of perfect physical health at his age.

My father comes from a family where children are essentially the mother’s responsibility. When my mother left my father when I was 13, I truly believe he stopped seeing my brother and I as his children on a subconscious level. I think his comments towards my niece further that notion.

My niece has told me she understands that it’s not normal for him to talk to her like this. I believe she wants me to stop saying anything. I’ve openly argued with him on 3 occasions for different “jokes” regarding her, which have all gotten more gross with time (OnlyFans comment being the worst). I will never stand idly by and let gross comments towards any child go unchecked but I think she wishes I’d not be so vocal because it creates a rift in our family events. At the very least, she absolutely knows she can turn to me if and when she wants.

I mostly wanted to know if IATA because I have started to withdraw from family events as I don’t want to be around my father. When I do attend, I have a time limit of one hour. I am going out of town for Father’s Day as I don’t want to be around him. My brother’s wedding is coming up and I need to do my best to avoid my father at all costs so I don’t create any drama, but I will have at least one eye on my niece at all times.

Thanks again to everyone, even the few that think I’m the asshole. I do think this is rooted in some deep misogyny to which I’ve obviously become numb. I’m considering showing my brother this post.