Astrid I hope you don't mind me responding. The "I don't remember saying that"... Is typically a PA thing. It is not honouring or respecting your boundaries but doing so "passively" by stating a lack of recall...

How you respond is up to you. It is very very very usual to respond in a PA way. Because you are not having an adult conversation. You are thrust into the parental role & he takes the child. This takes more effort and insight to navigate. I've been there & I totally get what you are saying.

"I've asked you not to slap my back with my bra strap". "MY body is mine, it hurts me, I feel humiliated & disrespected". (this is an adult response)

I imagine him saying: "well aren't we touchy today!" "You've never said this before so how would I know"? (or insert your particular PA's favourite response!) "why would something like a bit of fun get up your nose so much"... "Gosh you're touchy, you just don't know how to have fun anymore"...

You could then respond with something like: "I hear you believe you've never heard this before, so next time please remember that it's not okay with me"...

Don't be drawn into the argument any more. If he continues... "I don't have any more to say that's constructive right now"... "If you still need to talk about this please let's do so later"...

Sometimes it's necessary to leave the room, or the house - go fo a walk etc... The difference with being assertive and PA is that you: a) own your feelings... "(I am feeling anger coming up for me") remembering always your emotional responses whilst they may arise quickly are yours & you should not level blame at the other for your feelings.
b) if you need to physically remove yourself you do so but you communicate verbally. (I need to go for a walk to let off steam)
c) "because of how I am feeling I need half an hour alone to think" etc etc whatever it is you personally need.

This is why for me it isn't true that PA is evil. If we truly examine our daily responses we will often find we all use it in some times. Times of anxiety, stress & often when dealing with a PA response in another person - this is when it becomes especially challenging. So please be kind to yourself...

PA is just one of the many challenging traits that we learn through our childhoods especially. There are many others that some would find much more disturbing.

There is a really good book that I used to use when I facilitated unemployed Youth training in personal development. It's called something like "Are you an Emotional Vampire"...
That's not it - I haven't got my copy any more so I will have to rethink it.

It actually helps to identify not only in others but in ourselves what less wonderful traits we might use, name them & learn about them.

Some are very obviously distructive. Some like PA are much more insidious... I hope I've helped some.