Hi A.,
I strongly agree with the other posters that your son should not be playing and/or watching violent video games with dad. I myself am an "xbox widow" (j/k) and my husband and I have discussed that our son will not be allowed to play or watch violent video games. Even when he was only a month old and fairly oblivious I didn't even like him to be in the room when my husband was playing some of his games.
But more importantly than the video games is the way your husband is treating you. A majority of the time boys treat their moms (and their future wives) the way they see dad treating mom. So your husband's current example to your son is a lack of respect towards you and all future women in his life. So it may be *easier* to just let this episode go, but by allowing your husband to treat you that way you're not only welcoming it to happen again, but you (and your husband) are teaching your son that it's ok to disrespect women and not take their voices seriously. Also from what your son said when you caught them playing he's learning that it's ok to do something as long as you don't get caught. ("oh Mommy, it doesn't matter because you couldn't see it.")
If you want an extreme example of kids living by these learned behaviors just watch any episode of that Nanny show (the one with the British nanny chick). I've only seen it twice and it made me sick both times the way those kids treated their moms.
So don't be afraid to stand up for yourself. Do some research on parenting and get some outside help if your hubby really won't listen. Maybe he won't listen to you because you're too close to the situation and maybe he really doesn't respect your opinion like he should. (MEN! I tell ya!) But maybe you could find someone to talk to your husband about the fact that he doesn't just have a short little best friend living with you guys. This is a person that's been entrusted to you to raise into an adult. His actions might not seem like that big of a deal to him, but your son doesn't have any other life experience to go off of like we do. We are our kids' moral compasses. They look to us about how to act and how to treat others. We can talk all we want, but to our kids it is OUR ACTIONS when we're down there in the trenches that speak volumes to their eager little ears. So you and your husband need to decide: what kind of person do you want your son to be? And you can't just TELL him what kind of person you want him to be, you have to SHOW him.
And a *big* P.S. I know this is WAY easier to say than to do!
God bless and good luck to you, A.!