In no order, the 5 that come to mind:
"Sub Rosa" - the ghost with the most isn't, and the scene where everyone whines about the caber toss somehow manages to be even more embarrassing than Picard mulling over the dirty diary.
"Justice" - planet of the baby oil fetish is just pure cringe that tries to sell extremes for the sake of (eh, engaging?!) drama.
"Force of Nature" - the 55mph in space episode has an idea, but the execution is all over the place. But it has been a long while since any Trek reminded the audience that space is a big place and if the ship stops working, they're in deep doodoo. And this one still did a far better job at it than:
"Disaster". So many deliberate sidesteps with Geordi's VISOR, basic science principles*, and so on. Yes, we have to suspend disbelief over the ship, but - as with Space 1999's premise - overlook that and generally the show kept to specific rules. TNG5 often eschews them while wanting to play with "real world" ideas. To compare, the excellent "The Next Phase" is not mingling too many grounded ideas with the fantastical ones and, at least for me, holds together far better. It also has Romulan guile and some surprise twists whereas "Disaster" is so by the numbers...
"Emergence" - at least it's not another family member for Data being trotted out, at which point it'd be far worse. That got hokey as early as season 4. Also, for the sake of keeping the count low, a lot of "Data fam" episodes are not being included, but they easily could be interchangeable with this one.
* To the point that I thought that it was worse than season 1, where the show was scrambling to find itself and thus gets a little more leeway. True, "Justice" makes dumbbells out of Riker and Yar, but that's early season 1 and that story already had some major rewrite action going on. But this adventure is well into season 5, with very established traits and abilities featuring Beverly and Geordi, and the episode wants the audience to believe this is still early season 1, just with frog fart muzak in the background. It's beyond embarrassing that "The Naked Now" got right what Beverly and Geordi got wrong with "suck vs blow" regarding depressurization, inhaling deep before depressurizing (OMG, TOS episodes from the 1960s were far more conscious of basic real life science stuff, even that The Alternative Factor episode) . So yeah, "Disaster" DOES top my list at this point, period.
Dishonorable dismentions:
"Data's Day" - I still adore the basic idea of a Romulan spy winning the day and this episode just about manages it with that banger of an ending, but... the plot convenience to have Data overlook the spy is a little bit much... plus, the attempt at humor with the O'Briens felt clunkier as well. But with 26 episodes per season, there's room to try numerous format styles and this one got the humorous bent.
"Code of Honor". The script being too inane to give her name aside, one of many issues that make it "early season one caught-in-the-middle bystander", the actors involved do much to try to improve the cringeworthy dialogue, Yareena is genuinely cool (the actress's interview on the story is also worth a listen) and I also liked the fight scene, so to me it's not "worst ever" as much as it is a misfire of ideas combined with one or two setpieces, some of which feel like TOS rehashing. Probably bottom 50, or bottom 10 if it weren't for a lot of seasons 5-7 taking up that space already. That said, the idea of the leader of the alien world keeping true to his code whereas Picard is flagrantly violating it makes for an interesting concept. Having Picard order a volley of torpedoes over the atmosphere to terrify the population with was... pretty awful. But, again, season 1. Season4 onward should never have anything coming close to season 1's awkwardness and there's more of that than you'd expect.