The awkward situations where this has happened to me, my wife has been totally oblivious that she was being "hit on." I'm usually the one who mentions something like, "You know that guy was hitting on you." Her honest reply is usually "No, he wasn't." Followed by a "You think he was?"
I used to have a jealous reaction, but over the years I've come to realize that I have nothing to worry about. My wife is a very social person, but flirting with other guys is something she would never intentionally do. On the other hand, flirting with me . . .
We've been married for almost 9 years and our relationship couldn't be stronger.