"Oh my god this school is phiz."
"'Phiz' Miss Alvarez?"
"Well if you want to rewind the past to the beginning of the millenium, it means crap. But if you never even knew that, then I'd have to say you're a bit slow on the lingo."
I wouldn't explain.
Other people have mentioned
Clockwork Orange, which is pretty much the gold standard for this sort of thing. IIRC, Burgess didn't even want to include a glossary in the back. He wanted readers to learn by immersion or not at all. Of course,
Clockwork Orange isn't exactly the easiest book to read . . . I have to admit I'm more comfortable with a
Watership Down level of "alien"* vocabulary. Although in one of my WIEs (Works in Editing, of course) I've tried for a bit more. I do cheat by putting useful definitions at the head of the chapters, but no explanation in the text itself.
For the most part, though, I think words will explain themselves. When a teenage girl flops back on her bed and says, "My
God, my parents are twanks," do you really need a definition? If you had a time machine and a universal translator, you could hear the exact same sentiment in ancient Egyptian. If you wanted to.
Izunya
*Okay, so the characters in
Watership Down aren't aliens. They're rabbits. This, plus the fact that it's based on the
Aeneid, generally gets you very strange looks—but it's a remarkably worthwhile book, despite the premise sounding completely wonky.