BOOM.
As a police officer once told me, "all it takes is one WRONG WORD and you will strike someone."
In the addled brain of a perv, he sometimes thinks women want what he is doing - even if they don’t say it out loud. He may have seen her as being sexual because he obviously sees even young girls as sexual objects. Perhaps he conveyed to his son that the wife was a floozie, or maybe both men are just nuts! It still defies logic that the father would admit on camera that he was banging his daughter in law.