In the rush of learning, slang just slips in like a Game of Thrones fuck scene. It doesn't seem out of place because it's just another word you've never heard or used before, no different from any of the other dozen you learned that week. So if you grew up in the '60s and '70s, a term like "groovy" or "hunk" didn't seem like the unwashed underwear stains of language ... it was just another sequence of letters you didn't know yesterday, but do today.
Far out, kitty cat. Wanna get baked and give my dick a righteous disease?
The Warning Sign:
I mentioned that you never stop learning words, but there does come a point where the frequency slows to a near stop. And when a new one pops up, you can tell if it's real or just made-up bullshit. For instance, when I heard the aforementioned "hubris," I knew it was a real thing before I filled my clipboard and opened up Google. It didn't sound "clever" or edgy. It didn't have some ridiculous spelling. It didn't sound like an acronym or a shortened version of a longer word. But the first time I heard someone say "probs" in place of "probably," it took every ounce of willpower I could muster to not punch them in their stupid goddamn lips for having made that noise.
I also renounced the very air that made sound waves possible when I heard the first dumb asshole say "cray cray" instead of "crazy." Even widely accepted ones like "veggies" make me want to grab the person saying it by their neck and scream into their face, "YOU ARE AN ADULT!" Even if they're not.