Code of Honor--that racist episode with the space Africans?
Jonathan Frakes HATES that one, and for good reason; it was just plain BAD. Racist, sexist, nonsensically written, the fight scene was awful and ridiculous, Yar was so poorly written that I think that was the clincher that made Denise Crosby quit, and the entire mess was clearly Gene Roddenberry not having anyone to say "No, boss, that's stupid".
I'll definitely support that as the worst episode of TNG ever. However, if I recall, it was not Gene's idea to have a "Planet Africa." If I remember correctly, it was the director of that episode who was at fault, as the script originally did not call for an all-black populace; that was something the episode's director insisted upon.