what a mess!
first of all, START by telling him "DAD, why are you DOING this? i'm your DAUGHTER." that is a wake-up call, (unless he doesn't get it, or does get it and doesn't care.)
my primary advice with inappropriate behaviours is to treat them as inappropriate behaviours.
my mother often acts like a naughty child, and when she does, she gets treated like one!
back when your father-in-law was a womanizer, or "ladies man," i'm sure he got more than a few bad reactions. let me guess, he only does it when the two of you are alone?
five years ago, my mother was in a memory care assisted living for six months and was harrassed by several men there. administrative intervention did no good. my mother knew she was only there temporarily and didn't want to cause the eviction of these men. she was higher functioning than they were, and she knew it.
she explained to me that in their minds, only one response would put out the fire - a good slap across the face... she was right! they stopped. one slap did it in most cases. in one case a private slap was not enough. but after a gentle but humiliating public slap, the behaviour stopped
with your father-in-law, if you sass back at him or speak to him firmly (as though you are untouchable,) it will only egg him on. in fact, there is no verbal retort which won't. so my advice - prepare yourself - is to slap him across the face as though you are an army hospital nurse. tell him to keep his hands (or his dirty thoughts) to himself. THEN walk away. ideally, this will happen when he is stuck on the toilet or wherever.
if you cannot bring yourself to do this, the other approach i use with my mom when she does things that make caregiving impossible is to remind her that the ONLY thing standing between her and a NURSING HOME is ME. THIS my mother gets right away, and she ALWAYS chooses her cozy life at home with my family, and becomes compliant.
please don't be shocked by this. instead, hold onto your rightful shock at his behaviour, and everyone else's apparent lack of concern over it...
c.suzanneMcable2009