If your best friend tells you that you've become a snob, he means that you've become condescending and you like to think you're better than everyone else. Of course maybe he's a snob for looking down on your behavior — how annoying!
Snob has a funny history. It used be slang for "shoemaker," then "common person," and then came to mean "someone who doesn't have a degree from a fancy university," and then it started to mean "people who liked to pretend they have degrees and are generally fancy and look down on common people like shoemakers." Nowadays, snob isn't only for people with false pretentions. Rich people who despise less tasteful folks are snobs, too.