ESME... I am a male, and I actually encountered a similar situation on my second clinical rotation. My female attending, who was relatively young/divorced/with kids, would always flirt with me, telling me how attractive I was. She often suggested we go out for coffee, and I would just blow it off. After a couple days of working with her, she asked me to lunch. I didn't think much of it at all since I figured we'd just go to the hospital cafeteria together. Then, she told me to page her since she left for clinic in the afternoons... that way she could come pick-me up at the hospital (to actually "go out"). A couple days went by and I made some excuses. Then she said she wanted to go to dinner instead of lunch, since I was obviously busy during the day (aka, blowing her off). I realized, that things would continue to escalate unless I put a stop to it, and I kept thinking about how to handle it appropriately.....
I had absolutely no interest in this woman, but felt the "power" thing lurking over my head. I didn't want to piss her off and I also didn't want to make a stink over the issue. Most importantly--I did not want to go out with her. I finally realized, that if I would have gone out with her, it would have only been to appease her... which is not right, and would only feed the fire. Although she was not shady, like the attending in your situation seems to be acting, she was still acting "inappropriately".
In the end, I decided to be straight forward with her.... I went up to her one morning before rounds (privately) and told her that I was very flattered by the fact that she was interested in me, and that I really took it as a compliment. Then I told her that I was not interested in going out to dinner or lunch with her because I felt "uncomfortable" with the situation. I told her that it wasn't a big deal, and downplayed it everything else.... The second I said that I felt "uncomfortable", I could tell that she got a little nervous... She was probably thinking "****... sexual harrassment" in her head, but the situation was over, and she and I went back to normal.
I never told anyone (except one of my close friends in med school) about the situation until months later, b/c I respected her, and she was nice, and the last thing I wanted to do was hurt her reputation or EXPLODE the situation with gossip....
I would suggest doing something along similar lines... do not explode the situation with a "formal" report, unless you're forced too... I would causal explain your situation to him and tell him you feel uncomfortable with the situation. If he is normal, the situation will stop. If he does not, then file the report... but realize this will EXPLODE things, and you'll be hearing about it for the next 2 years... And it will always be on your mind. If you can drop it, I would.