What to do when the dementia causes the patient to start making sexually inappropriate remarks?

GET PROFESSIONAL GUIDANCE.

I am so, so sorry you are having to deal with this, but please note I am equally sorry for both of you - you because it is absolutely harrowing, and your father because his dignity is in tatters.

But there are techniques and strategies for managing all "challenging behaviours," and they can be learned. If they're not enough then you will need to consider placement or full-time support at home; but, as I used to ponder when I was bed-bathing my mother and changing her continence care pads, it is amazing what you can get used to.

So - this may turn out to be your red line and you would have nothing to feel guilty about. But it may turn out that you surprise yourself with your own strength and depth of understanding, and get through this horrifying phase in his illness. Either way, we will be here to support you.

Margaret is right. My mother, always a prude, was obsessed with sex when she went to a facility. Not her own sex life, but everyone around her. As Margaret writes, don’t be terrified and consider the source. His brain is broken and he truly doesn’t know what he’s saying. However, if he is mobile and strong, you may want to consider a facility.

With my mom, I just kept repeating to her, “Be a lady. Ladies don’t talk like that!”

There may not be much you can do about it, except stay out of arm's reach and ignore it. Or find a care facility for him. It isn't uncommon. Please don't be terrified. It isn't justified and it doesn't help either of you. It is almost as though it happens more frequently when it is 'out of character' - perhaps even dirty jokes have always been repressed, and the dementia lifts the lid off years and years of trying not to say the wrong thing.