Yes, if I'm in a casual situation like shopping or eating at a restaurant or working or w/e, and I don't expect to be looking for women, it's almost impossible for me to pick up on it in time to react. It was terribly embarrassing as a teenager walking around shopping or eating at a restaurant and having my MOTHER tell me "oh that girl was trying to flirt with you". I usually lied and said I knew that but wasn't interested in dating. It was true that I wasn't interested in dating as a teenager (too much work and I didn't get along with teenagers).
Sometimes I do realize when a girl is trying to flirt, but when I do it's several minutes, hours, or days later. Obviously, this is not notably helpful except as a way to learn what people do to flirt. Perhaps as a result, I can pick up on flirtation in one on one conversation if I'm on a date or in some situation where I'm expecting it. It's rather like I know what to look for, but I have to tell my brain to anticipate and look for it, or it won't register. My normal mode of thinking is that I basically screen out everything that's not directly relevant to what I'm doing at that moment. I have to work somewhat to maintain awareness, or be so interested in a person that they actually command my complete focus.
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Self-Diagnosed Dec. 2010
135 Aspie, 65 NT--Aspie Quiz
AQ 40
BAPD--124 aloof, 88 rigid, 83 pragmatic
EQ/SQ--21/78--Extreme systematizing