Caleb Crain explains the value of modern slang:
One comes a little closer to a definition of slang by thinking about context. Dirty words suggest that the audience is no better than the speaker, and vice versa. Slang, on the other hand, usually suggests that speaker and audience share membership in a group. A prostitute who describes a slow-to-satisfaction customer as a thirty-three, thereby analogizing him to the standard speed for long-playing vinyl records, is probably not speaking to a police officer. A gay man who describes a lover with a similar quirk as long-winded is probably not speaking to a heterosexual. The implied identifications are flexible, however. If a gay hairdresser in London offers to zhoosh you, it’s safe to accept his titivation even if you’re a straight man. The word might make you blush, but it won’t compromise your orientation; it merely dignifies you with honorary membership in the group of people who understand how he talks.
The Dish 