The best kind of comedy is the kind that demands a second viewing. Some jokes fly by so fast that even if you laugh at them, you don't appreciate the true depth of the joke until you hear it twice. Community is the god king of this kind of comedy on television.
Which should come as no surprise given that this show was created by the all star team of Dan Harmon and the Russo brothers, two names that pretty much everyone knows these days thanks to their work on Rick and Morty and the MCU respectively. But Community was their first big hit, and it has all the trademarks of both creators.
Most of which you notice upon rewatching the show now that it's all on Netflix. This irreverent, cartoonish sitcom hid a LOT of details in the background of the show's plots, a lot of which require careful combing through individual episodes before finding them.
These are the most interesting things you learn from that effort, whether they're bizarre, interesting, or just plain hilarious.