Oh my god, I'll try to explain but I don't know if I can.
There is this trend of meme going on for a while that has the format where a teacher tells the class "ok class, it's time to finger paint". And the joke is that there is one kid in the class named "paint", so the implication is that the whole class is going to finger him.
On the okbc sub, there was a recent trend of memes poking fun at this kind of meme, where the setup would be something non-sensical, and then the punchline would be an image of Mike from the show with the words "kid named finger". The joke here is that it really doesn't make any sense, so it's more of an anti-joke than a regular joke.
I hope you at least got a rough idea of what the joke is about. Trying to explain this shit has got me on the verge of a stroke.
