Just about the entire script of "Let That Be Your Last Battlefield," is cringeworthy, but this exchange pretty much sums it up:
LOKAI: You see, you are from the planet Earth. There is no persecution on your planet. How can you understand my fear, my apprehension, my degradation, my suffering?
CHEKOV: There was persecution on Earth once. I remember reading about it in my history class.
SULU: Yes, but it happened way back in the twentieth century. There's no such primitive thinking today.
Subtle as a wrecking ball.
First one the comes to mind . . . "Double Red Alert!"
Which episode was that in? Makes me think of "Double Secret Probation."