As for the original question, I really cannot tell when I am being admired or hit on. I usually do not like attention, so I tend to be able to blend into the background quite well at social events. I only know when my friends tell me after the fact. Here is an example:
When I was in grad school, the university had a gathering for professional students at a local club. Against my own interests, my friends dragged me to this party to play wingman for them. I was very bored with the social chitchat, so I sat down at a booth and started working on a research paper that I needed to write. A woman sat down across from me and started to question me to death. I did not think anything of it and answered her questions about my studies at the university. We talked for an hour or so and then we had to leave as the party was over. She parted ways and said it was nice meeting you with a wink.
My friends were bugging me about getting her number, but I did not. Turns out, they were all trying to hit on her earlier, but she was not interested. She ignored them and spent the majority of the time talking with me instead. They said that all her attention was on me the whole time. While she was very pretty, I was still concentrating on getting my work done on the report in my head. It never crossed my mind that she was actually interested in me. Being severely bullied in my youth, I do not have a good self image on social things so I could not fathom that part. My friends were so pissed at me and they would not talk to me for more than a month. They called me the nickname clueless for a long time afterward. My brain just does not function in that realm.