There will always be exceptions. But the odds are not stacked in the PUA's favor for this one most specially for
still uncalibrated newbies. Approaching a stranger from behind who didn't give you any eye contact at all and then immediately slapping her butt is a bad idea.
If you are Brad Pitt or Justin Bieber, where you have initially built lots of comfort with millions of women around the world through your movies, videos or songs then approaching women from behind and slapping their butts is okay.
A pretty good pick up line in my opinion is something that immediately makes the girl comfortable with you AND allows you to immediately transition into very sexual nonverbal and verbal conversation.
I only slap girls' butts AFTER they have given me the eyefuck and the results were always good; even great at certain times.

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Approach. Open. Escalate. Isolate
Here are my two essential rules on texting that will save you tons of time and money:
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