Forget the psychology behind it all ... you'll just get tripped up on mostly-wrong and vague theories.
Look at the social-psychology behind it all (social coming from sociology). Social-psychology is a FAR better study which will allow you to read someone and play on their body language. Furthermore, you can actually change how people feel about you through subtle changes in your own B.L.
All said, psycho-poop-ology is a very interesting bathroom reader (says the former social-psychology student). Pun intended.