Boundary violators are given 'the benefit of the doubt' when they should be given responsibility for their actions. Often, someone will state their boundaries repeatedly and have them repeatedly violated by someone who then repeatedly claims misunderstanding. This doesn't happen with someone who genuinely wants to avoid violating other people; they become increasingly cautious if there are multiple occasions of the same mistakes, and they try new things to prevent those mistakes, like asking more clearly, or asking only in particular situations, or using code phrases or gestures, or seeking educational materials on consent.
If they violate your boundaries, you tell them that this happened, and they do not change their future behavior to prevent this happening again, they do not care that they are violating your boundaries. It is okay to call them on this. You don't have to give them the benefit of the doubt and assume that they didn't get it just because they said so. If their behavior does not change significantly every time they make a boundary 'mistake' it is NOT A MISTAKE. They are CHOOSING to not learn* in order to claim ignorance as a defense for doing whatever they want to do.
Let me say again -- if you have had more than two boundary violation 'misunderstandings' and the person hasn't shown any initiative (read books, asked questions, changed habits) to learn how to be good at consent, they do not want to know. Which means it is not an innocent mistake, because when people do things that they actually consider wrong, they put in safeguards to prevent the mistake happening again.
That is a tactic I have seen over and over -- it's a cheat that allows the person to avoid consequences, including guilt. With this tactic they don't even have to feel bad for violating boundaries; in fact, they usually blame the victim for not teaching them better in the first place. It works on compassionate people because we always want to excuse an innocent mistake. It works especially well on people who were socialized as girls, because we are trained to be helpful and nurturing, to teach rather than evaluate. People can act so distressed and apologetic for boundary violations, yet if you look carefully, it is just obedience to social scripts that say "apologize when someone is upset" and not any ACTUAL apologies which involve making things better for the future.
*there may be variations on this for people with cognitive disabilities -- it may take them longer to learn, but if they are sincere, then there will be noticeable efforts along the way.
[TW: brief but specific account of rape]Emma Lindsay writes about this tactic (TW: link contains descriptions of rape) -- "...despite whatever lie he told me or told himself, he knew I didn’t want to have sex with him. He knew I didn’t usually lie there like a dead fish. He could tell when I was wincing in pain. When I told him I had been in pain afterwards, he showed no surprise. I had only articulated what he already knew but was pretending he didn’t."