I'd just like to share a little something I learned, which may very well not apply to you at all.

I was hanging out with a friend of mine, and she could tell every time I was checking out a girl, nearly instantly, even when I was trying to be surreptitious. Tips she suggested: move your eyes and not your head so much. Also, girls have better peripheral vision apparently. Oh shit, all those times I was staring girls up and down while I was turned to the side and they were facing forward. It's like being told my mirror actually broadcasts on some live stream.