Brood get laid then post plox ... You're like my 24year old friend playing WoW 24/7, talking about chicks as if he were a pornstar...
As per OP's question, i used to get the same thing when i was younger and i couldn't quite figure out why... Till i had numerous females in my life and had built up some self esteem. Not to say that yours is low but in my case the trick was to stop seeming like you're trying not to look invasive and trying to seem like you're not looking at them. Even if you are successful at the latter, the women in question feel what the buzz is about and act as though you're about to stalk them. Now in these situations if i happen to look at some females beside me i don't hide anything and loom them straight in the eyes reading them through till demolition. Most look down and somtimes blush(insecure attention whores ), where a more experienced woman or simply one that is confident and worthwhile may actually become interested in you.