In "Custody" (TOS, 6x14), Robinette (as defence counsel) informs the trial judge, Judge Cyrus Metcalfe, he [Robinette] will be filling for the judge to be removed, because "Three years ago, over dinner at Elio's, you said all drug addicts should be rounded up and sterilized. (...) And if I subpoena him, so will Ben Stone. We nearly fell off our chairs when you said it."

Usually, I know which prior episodes are being refered to, but this one is driving me nuts. I've checked on here (this Wikia), IMDB, and even Wikipedia, but I can't find any mention of the character being in an eariler episode, nor do I remember either a judge ever saying something like that or even Stone and Robinette going to dinner with a judge.