We soon come to know when and where it is appropriate to say certain things, to use certain words, to discuss certain topics or wear certain clothes, and when not to. Such knowledge about cultural norms is important for impression management, which is an individual's regulation of their nonverbal behaviour. We also come to know through experience what types of people we can and cannot discuss certain topics with or wear certain types of dress around. Mostly this knowledge is derived experientially.
I'm going rollerblading around town, rocking acid washed jeans and a fanny pack, smoking a cig, handing out free candy to children...