Ugh, Once Upon a Time is "THAT ONE EPISODE". You know, that one where you'll be channel surfing and tune into a show you only casually watch in reruns and it's the one you seem to see over and over and over and over again. Every time I'd tune into Voyager on Space it seems like it would be this fucking episode.
For DS9 it's that stupid early season episode where they get turned into game pieces in some Gamma quadrant alien game.
For TNG it's the rad episode where Picard and co come back to the Enterprise frozen in time in some incident with a romulan warbird. (This episode rules)
For TOS, it's Who Mourns for Adonis? The greek alien space god episode.