Fear/suspicion towards men is not really an uncommon thing, and it isn't always due to abuse. Tasha is very fearful and suspicious of any man she's not really familiar with and she has never been abused by a man. When I got Raven, she was a bit more shy and backed away from bigger men at first, but I socialized the heck out of her and she's fine now with all people. As my vet stated when we talked about it, men are often bigger, deeper voiced, and just a more "threatening" presence to a dog than women often are. Women are just usually not as threatening, they often have a smaller stature, softer voices, and body language that is more reassuring and inviting to a dog when meeting a stranger. Tasha warms up to women much, MUCH faster than to men. I'd have FIL ignore him totally when he comes over for now. No eye contact, no talking to him, not even offering his hand. When he sits down to relax and if Rocky approaches him then, he can probably nonchalantly greet him then after that, while he's in that less threatening/relaxed position. Of course none of us are there to actually witness the behavior so a consultation with a behaviorist if you find this concerning would be a good idea. Just my 2 cents.