I used to flirt all the time and enjoyed other people flirting with me, as long as it wasn't serious. If it it became serious I would fall apart. So being able to flirt is clearly about self confidence. However being flirt blind is all about perceiving yourself as attractive, as someone worthy of attention. I miss women flirting with me because I right now don't see myself as attractive, lovable - yes, attractive yes-ish. The other thing that definitely makes you more flirt blind is depression. firstly as you feel less bouncy and interesting to others, secondly you don't notice others flirting with you.

hope this helps