My own nominee.
Yes, but this was one of the unambiguous “Kirk got it on” episodes, which is worth something. (Kirk and Deela in his quarters, fade to black, return from commercial to find her brushing her hair while he is sitting on the bed zipping up his boots.)
It’s been a long time since I’ve seen most of these, but this is how I remember it: “Spock’s Brain” was bad, but at least it was amusingly bad. Plus, it gets a reference in Semisonic’s (IMHO) best song “Never You Mind”:
The title was “Wink of an Eye,” and yeah, Kirk definitely got laid in this one! 
Trivia: The same concept (chemically accelerated villains) was used on an episode of Wild, Wild West; I believe both episodes were written by Gene Coon (on ST, under the pen name of Lee Cronin).
Klingon, puh-lease! If I were anything, I’d be a Romulan, as they were originally conceived: Vulcan offshoots with an honorable culture resembling that of Imperial Rome. On TNG, they morphed into something quite different since the Klingons had been elevated from pond scum to noble (if somewhat dim) warriors.
I’m surprised no one has mentioned “Spectre of the Gun,” which is usually found on people’s lists of bad episodes. Actually, I quite like it, as it’s based on a very science-fictiony concept. IIRC, it was also the first episode filmed for the third season, before the true rot set in.
I’m also inclined to disagree about “The Omega Glory.” It was a fairly good episode up until the fourth act, where the combination of heavy message and Shatner’s overacting ruined the whole mood. It should have ended with Kirk beating the crap out of Tracy and the lot of them vanishing in the transporter beam, to the complete and utter amazement of the Yangs.
“The Omega Glory” also has Spock using mind control, for the first and I think only time, from a short distance but without touching someone. Vulcans aren’t supposed to be able to do that.
Anyway, “Spock’s Brain” gets my vote. Hoo-boy, that stank! Quite the steaming pile. One of the first eps I ever saw, as it happens - good thing I kept watching.
I kind of liked “Return of the Archons”. No votes yet for “Savage Curtain”? Abe Lincoln on Star Trek? C’mon!
“Limited telepathic capabilities are inherent in Vulcans.” I forget in which episode Spock said this, but he did. Physical contact is required only when they need to make full mental contact with a corporeal being like a Horta or an AI like NOMAD.
Even more trivia, before Star Trek and Wild Wild West, the 1963 movie musical Bye Bye Birdie had a scene where an orchestra was chemically accelerated to save a plot-important three minutes. To the best of my knowledge, Gene Coon had nothing to do with it.
There are 26 posts in this thread and no one has mentioned “Let That Be Your Last Battlefield”? That unwatchable polemical klunker with the blackwhite people at war against the whiteblacks?
John D MacDonald also had fun with the concept in The Girl, the Gold Watch, and Everything, though there it wasn’t chemically induced. I think it’s a pretty common thread in SF and has probably inspired a number of writers.
Spock’s Brain. It is fun, with DeForest Kelly trying to out-Shatner Shatner (“A *child *could do it! A child. could. do it!”), but you can say *any *TOS episode is fun.
***Eden ***is bad, but it’s got the Vulcan harp, and I figured out how to play their jam song on the guitar, so it’s special for me.
As a kid, I found that one really haunting. The idea of fighting somebody literally forever kept me awake nights thinking about the void.
I find it worth watching just to see Frank Gorshin running through the ship’s corridors in his pink tights. I keep waiting for him to jump out of the turbolift and shout “Riddle me this, Captain Kirk…” 
Supplemental: He did it in at least two other episodes, “A Taste of Armageddon” and “By Any Other Name.”
The thing about Last battlefield; If the Gorshin character were to look into a mirror, he would see himself as the other guys.
At least Catspaw had the Spock line, “A bit more alacrity if you please.”
I vote Spock’s Brain.
This. It may be a turkey, but it’s a FUNNY one. And it does have some interesting points to make.
In fact, I can’t help but wonder–this was written and broadcast BEFORE the Manson murders. Given Trek’s propensity for writing parables of real-life problems, if this had been written afterward (for a hypothetical fourth season, say) we might have gotten an entirely different kind of story about a charismatic leader with lost youth under his spell.
Getting back to the funnier side of things…whenever I hear that one hippie kid’s rhymes, all I can think of is Dick Shawn’s L.S.D. character in the original Producers. I don’t know which is funnier…L.S.D because he was supposed to be funny, or Adam because he WASN’T.
I guess I’d rather be a Herbert than a Dunsel.
“I don’t understand why a young mind has to be an undisciplined one.” -Scotty
Spock always had whatever magical powers the story demanded. Super strength, telepathy, super hearing, second eyelids, katra, etc.
You’re ALL crazy. Stop mentioning episodes with some redeeming value as the worst. Herberts.
It’s “And the Children Shall Lead”…btw.
Well, call the angel, that ep blowed. I agree it’s bad but I stand by “The Empath” as worst.
Heh. During the Crown Heights riots in NYC in 1991, SNL’s Weekend Update anchor (I think it was Dennis Miller) joked that the mayor had ordered a marathon rebroadcast of the episode to improve race relations in the city.
Really? Remind me of the circumstances, please.