You guys have brought up great points. Was nice to read it.
For me I've had small and big confidence issues, and as lucio said, thinking what others think of you, consciously and unconsciously plays a big part in how you deal with it.
I found a small start to pushing past it is to look people in the eyes when you talk to them (I never noticed that I wasn't doing it till I really started thinking about it). Greeting people, again, look at their eyes. Walk tall (cliché, sorry), I always used to look at my feet/floor when walking. I don't know about how you guys perceive this one, but when on public transport, or something similar, if you make eye contact with someone, just give them a small smile.
It can give you a nice warm feeling if they smile back. (usually even greater when its a lady )
Lastly, I believe there is a balance, too much confidence and you are one of those chumps who you can easily despise.