Paris and Janeway, as lizards, doing the space sex, because they went too fast.

My vote goes to that episode in season 1 of TNG where they're fighting black people on like a jungle gym.

Neelix and Kes when Kes is essentially in heat. That episode was so gross

Almost any scene in the decon chamber on the NX-01.

I'm going to say any space battle scene made since 2009.

From TOS up through Enterprise, you could follow the space battles. "This ship went this way and fired phasers but it only hit the ship's shields, then they fired back..." Camera movements were smooth and comfortable, you could see and tell what is going on.

J. J. Abrams shows up and all of a sudden we've got panicky Saving Private Ryan cam and there's just nine layers of beam spam on the screen. Everyone is machine gunning everyone from every which way. It's got George Lucas syndrome. "Put more special effect bullshit on the screen. More. MORE. MOOOOOREEEEE!"

Star Trek: Picard, when the Borg wake up and the Romulans just vacuum them out. In that moment the Cube should have automatically teleported them back inside. If the teleporters were down for some reason, the remaining Drones would just happily continue working in hard vacuum and proceed to assimilate the shit out of the Romulans. What happened was an uncalled for nerf of the Borg.

Whenever Riker meets eyes with a female humanoid alien earlyish in an episode, you know exactly what the B plot is gonna be

The one where Dr Crusher has sex with a ghost

The "Allamaraine" song scene from DS9's Move Along Home.

https://www.youtube.com/watch?v=0FM6Xfs2ZoY

In fact that whole episode.

Anything involving time travel. It's the sci-fi equivilent of jumping the shark. There needs to be a viewer warning at the beginning of such episodes stating:

Warning! Our writers are currently out of good ideas. So, we threw this lazy shit together, which is going to be completely unsatisfying and will leave you with a vague feeling that the show should just end and let the writers move on to something new. Viewer discretion is advised.

As an added warning, any episode which involves going back to the real present day should end the above warning with 20 minutes of Bobcat Goldwaith screaming.

Tasha Yar dies due to the Exxon Valdez.

DS9. The Dominion is about to come through the wormhole with hundreds or thousands of ships and the prophets are like "omg Sisco you can't have a fucking war here, man, we need you later on" and Sisco was "fuck you, I do whatever I want, do your magic, I don't care, it's man's business" so Sisco wont retreat.

and then what happened?

The whole fucking Dominion fleet just disappeared, poof! like Sisco used some kind of cheat code.

fuck that.

anyway, it's not the scene itself that was bad, but man. that was so freaking cheap I think the whole show changed in me a little bit after that. still amazing series, tho

When Spock fails to get laid because he's a half-breed.

As characters I hate all Crushers and episodes dedicated for them.

...but there are episodes worse than those.

Janeway and Paris making lizard babies.

Every second of discovery