Dick was probably a dick on the outside too. People that feel powerless, whether they're incarcerated or not, try to find a way to exert power over others. having a loud obnoxious mouth is often all they've got to accomplish that. And being locked up only amplifies the powerlessness they feel.

Next time he says your wife is probably messing with someone else, just laugh and say, "yeah, well, at least I know it's not you." (not actual advice, I'm not sure how that would play inside, but you get the idea).