The ';other'; woman is being friendly to your wife/girlfriend?

Just to get this straight, I'm sort of the other woman, but there's no affair here. He's a guy I like to flirt with from time to time. He's got a girl, and I've met her recently, we have mutual friends so we've talked at parties and the guy in question has been staring at us and I don't know what to assume. Do you think he finds me threatening or is he intrigued? I wouldn't do anything with him, I'm a flirt is all. I'm currently dating someone else anyway, I just found the way he was staring surprising. In a way I think he was enjoying it. Which is just weird. I'd expect him to feel uncomfortable. So how would you feel if you were in the same situation?The ';other'; woman is being friendly to your wife/girlfriend?
Too much drama!!