I am Captain Oblivious. It's unlikely I'd even notice.

Not quite the situation you present - but comparable :

I was at a family gathering, with my then boyfriend of a couple years. While we were all mingling in the kitchen, his Uncle came over, said hello a bit too friendly, and touched my butt - definitely deliberate.

Without saying a word, or being obvious, I reached back and caught the offending hand, and bent one finger back - just enough - then let go. I met his gaze then - without smiling - he got the message ... it all happened quickly - no one else was aware.

id flirt back

I could never respond in kind because it goes against who I am. This goes against my ethical beliefs. I could never intentionally hurt a friend like that. That's just who I am.

Since my last ex was a closet philanderer, and i was (according to "our" doctor) exremely lucky to have escaped healthy, I would become pretty upset with the dickhead. Of course, if it was just a drunken one-time verbal teasing, I would do my best to forget it. Otherwise I would go right to the wife! I WISH someone had wised me up! Amazing how everyone had no trouble laying all the crap they knew about him on me After I found out....gee, thanks?........

Depends on what the house rules are and what level of flirting. Won't have a bar of sneaky behind the back stuff but have known both men and women who were horrendous flirts but didn't mean anything by it. Have also known people with open marriages so then it is simply a matter of whether you are interested or not.
Have also had friends husbands sniffing round after my separation/divorce in a manner that was definitely not OK in which case it was tell them to get back in their box in no uncertain terms. Never felt the need to tell their wives because they'd already got their dose of punishment because in those cases used to serve up a mild side order of humiliation to go with the refusal.

Be more specific about what is flirting