I think that when someone is self-conscious about something on their body/face, that they tend to take more notice of these features on other people.
For example, I am most self conscious about my nose and teeth. So I tend to notice these features on my friends, on people I have just met, people I don't even know, or people on TV more so than I would notice their hair, weight (unless it was really obvious), eyes etc.
I don't notice to judge them, but I notice to compare.
These sort of comparisons are probably not that healthy, especially when the majority of the time it will leave me even more self-conscious.
When I mentioned this theory to someone, they laughed at me and said they didn't even take notice of these features of myself I don't like. Which makes me think of different peoples perceptions. Such as one of my friends thinks she has a 'chubby' face but I have never noticed in my life, until she pointed it out, then I still disagreed.
It's funny what we have hang ups about as individuals within ourselves, other people may have never noticed. So maybe our noses, eyes, faces, mouth, teeth aren't as bad as we think they are? Or maybe because we are just so used to seeing our images, that we scrutinise it and pick out what we consider flaws so much easier than what another person would do.
Maybe it all comes down to having self-confidence or not caring what people think. Or maybe an individual, will always have that seed of self-doubt implanted in them, no matter what they look like to other people.