[ivank]

My untested hypothesis is that your parents and peers expect you to act a certain way (based on your appearance) and many people accept these subtle nudges without resistance. So, it basically becomes a self-fulfilling prophecy.

[ovi256]

I think that is a form of operant conditioning [1] mostly through subtle cues and social pressure.

[1] http://en.wikipedia.org/wiki/Operant_conditioning