On a lighter note, this has to be one of the funniest scenes in Star Trek.
This is from the episode, This Side of Paradise. The Enterprise is assigned to check on a colony on the planet Omicron Ceti III which is exposed to lethal “Berthold rays”. They are surprised to find the colonists alive and well thanks to strange plant whose spores not only protect them from the radiation but make them all mellow and content. After being exposed to the spores, Spock is finally able to let loose. The look on Kirk’s face is priceless. Sulu looks like he’s been drugged after breathing in the spores.
Kirk cures Spock by picking a fight with him, and nearly gets himself killed.
This is actually kind of a sad episode. Kirk, Spock, and the entire crew of the Enterprise find perfect happiness and contentment on Omicron Ceti III under the influence of the spores. At the end, Spock admits that he was happy for the first time in his life. He can freely love Leila, a woman who loved him. Yet, in the end Kirk and Spock choose their duty to the Enterprise and Starfleet over life on the planet.
Star Trek was made in the old days, when good values could still occasionally be found on television. I think that the theme of this episode, like several others, is one of choosing duty and responsibility over self-indulgence, and ultimately freedom over happy slavery (to the spores). They don’t make them like this anymore.