Real Slang vs Failed Attempts
The difference is not the word. It is whether anyone has to explain it.
The real side: crine, larping, aura farming, bussin - used in a sentence, no gloss, no apology. The user assumes you get it and does not check. That casualness is the fingerprint of real slang.
The failed side: yolo, fleek, on fleek, Bismillah c'est les ténèbres - deployed with visible effort, often out of date or invented. The moment a phrase is performed for an audience, it is no longer slang. It is a bit.
The test: could a 17-year-old say this unironically today? If the answer is "they would not, and if they heard it they would cringe," it belongs on the failed side.