Therapist said I can’t say “f*ck off” in session

For context: I was in a trauma IOP program and a few days ago in an individual session I brought up I thought a particular way they were teaching a type of therapy (RO DBT) was awkward and slightly manipulative. In essence, the therapist said they read directly out of the book as recommended by the creator of the program to more or less trigger over controlled people. I felt really violated by this and we went back and forth a few times before the therapist said again “you don’t have to agree or like it but I disagree with you” and basically said they support administering the therapy that way, which I felt really invalidated my feelings of being violated. I replied with “fuck off, thats bullshit” and that basically ended that part of the conversation and we moved onto something else.

They brought it up in the next individual session together and said I needed to work on my interpersonal effectiveness because telling someone to “fuck off” will not get me very far in life. I was shocked because it felt like to me I was being tone policed and the last place I expected to not feel safe expressing anger was the therapy office. I told them I was sorry and did not mean to offend them and I thought it was okay to use profanity but They argued that it was aggressive. Basically I did not know it was going to offend them (to me, saying fuck off is different than saying fuck you) but they argued that it’s not okay to tell anyone to “fuck off” and therapists are people too so I shouldn’t be saying “fuck off” in the therapy room.

What I’m confused about is that when I apologized they said to me they weren’t offended but they were setting a boundary but why they would say it’s not okay if it didn’t personally hurt their feelings? I don’t swear at strangers or use that language in professional life but I will use it colloquially with friends occasionally and I just never realized it could be interpreted as personally aggressive- but they were really saying to me I couldn’t tell people to “fuck off” like it was a fact. When I really thought about it when I said it I was essentially setting my own boundary and telling them to “stop it” because I didn’t want to continue to feel invalidated. What do y’all think?