I used to believe that a PUA was someone like Mystery, who claimed (at least in the book The Game) that he knew exactly what to do and say to get any girl into bed. I believed there were some "tricks" to use, as if it was all like magic. I remember stuff like BHRR (bait, hook, reel, release), cat string theory, compliance tests and other shit. Later I realized it was all BS and I found out about RSD and others.
RSD on the other hand gave me the impression that a PUA was someone who was on the top of his shit all the time, pulling girls every night, super-freaky-happy and extreme in every way possible, impossible for me to reach the same level of success as them. Impossible to become a "master". It took me a year away from both pickup and RSD to realize I was already there - I was already a "master" and had been that for a long time. And when I realized that, I thought "was that all? is it really this easy?". That was when I ditched the PUA title altogether. It doesn't mean anything. I know a lot of people who are just as good as I am, and they are true naturals. The only difference between me and them is that I consciously know what "the best move" is, and why, while they are acting "on instinct" so to say and can't really explain the process.
So to round up with my conclusions - a PUA is something you would call yourself for your ego. It is for people who - for some reason - think they are better with women than other guys and want to brag about it (and thus demonstrate lower value and fail more frequently).
