I have been fucking women in front of their husbands and boy friends all my life since I was a teenager. I don't love the situations where the wife is all about humiliating and verbal abusing the hub. I would much rather satisfy an unsatisfied woman, and let the husband's humiliation happen from what he sees. However, I have certainly seen my share of what you are talking about.
First, figure out what is really going on. Is she really angry at him out of her frustration because he does not give her the sexual pleasure that she needs? Or, is he really the one who just wants to be humiliated, and she is just going along. If it is the first case, all you have to do is cue her to tell him how great you fuck and how piss-poor he is. "Baby, tell him what this feels like.." How deep am I in you?" "Tell him how this compares to him" She will be happy to make her husband feel like the miserable little boy that he really is.
If this is really his great fantasy, and she is just agreeing to his humiliation only to please him, it is different. Ask her the same things, but you are going to have to do much more work. Tell him how big, powerful, good you are, and make her agree to his inadequacy. Make him look at you, keep his eyes on your size and superiority. I tend to make him do a lot of servicing, but you are not into that. Its a lot harder, believe me, if you want to do a good job. You have to be creative in how you insult him and make him understand how sexually useless he is. It can get pretty sadistic. I tend to let situations like this go after the first time, unless the wife is really smoking hot.