And as a more general point, I am really concerned that this act seems to be becoming more prevalent, with the acceptance of anal sex as a mainstream sex act.
I don't want to kink shame anyone and fully accept that some women greatly enjoy anal sex, and they should absolutely crack on with it. (Funnily enough I was part of a really interesting and useful chat about this on the sex board, which helped me understand that for some women it is genuinely great).
But a friend of mine has experienced what happened to OP twice with different partners in the last year or so - they have penetrated her like this with no discussion and no permission given.
Fortunately she is among those women who find anal sex comfortable physically (some do, some don't) so she has not actually been injured or even physically hurt. She did in both cases immediately call a halt to both the sex and the relationship, and was still shocked and angry that her partner's had thought this acceptable on any level.
I haven't had this happen thank God, but I have had a number of men try to persuade me that I will enjoy anal with them, that most women love it, many love it more than they like vaginal sex etc etc, with a subtext that I am somehow disappointingly "frigid" not to like it.....
I now make it clear to any new partner as soon as I know sex is on the cards, that I dislike anal sex and it will never be on the table. But it should be absolutely the other way round - consent to this act, that is painful for quite a number of us, should not be assumed unless we go out of our way to clarify it's not on the table. Because many women won't even think to bring it up, until it's too late and frankly, why should they? There should be no assumption of consent, to anything, ever.
I do think the prevalence of porn is giving rise to these dangerous expectations of what sex will be like. But that's not an excuse. Anyone old enough to have sex is old enough to know you seek clear consent for any act, and that if you get it wrong and think you have consent when you don't, that's your mistake, and not your partner's for not being clear enough. The onus must always be on the person performing the act to ensure it's welcome.
It's like me taking someone's phone and saying "oh, you left it on the table, I assumed you wanted me to have it". Even if I was telling the truth, that wouldn't make me any less of a thief.