#3: The Trouble With Tribbles
In case you forgot: The Enterprise is tasked with guarding a store of grain on a space station from Klingon saboteurs, much to Kirk's frustration. The overly-theatrical but still charming trader Cyrano Jones brings the fuzzball Tribbles on board the station and they end up reproducing at an astronomical rate, but they serve their purpose in uncovering a Klingon mole and saving the nearby planet from poisoned grain.
It's goofy, but it's a classic. Spock gets to deadpan snark EVERYTHING, Scotty punches a Klingon for insulting the Enterprise, and Stanley Adams is loads of fun to watch as Cyrano Jones. It's too bad Jones never made another appearance in the series, as he's just as much goofy Summerstock community theater fun to watch as Mudd.
I may have permanently ruined this episode for myself by reading up on Stanley Adams and learning that he died of a self-inflicted gunshot wound. I may have now ruined the episode for you as well. I'm sorry.
Back to the episode itself, though. Kirk is kind of needlessly dickish to a Federation official just trying to do his job. Whatever's supposed to be funny about it just isn't, at least for me. But then, if he weren't being a dick, he wouldn't be Kirk.
The overall silliness, while refreshing and fun, doesn't really have any emotionally satisfying "right in the feels" moments or interesting philosophical quandaries, making it mostly fluff and filler. Well-done fluff and filler, to be sure, but fluff and filler nonetheless. Nonetheless, it's a good palette cleanser. Some days you have moods that only Tribbles can fix.