This is bound to lead into some arguments, but what the heck?
1) 2008 - Indiana Jones and the Kingdom of the Crystal Skull - The fridge nuking.
When this happened, I felt like I was going crazy, like I was strapped down in a room somewhere hallucinating this, or like Spielberg was going to pull aside the curtain and say "Gotcha! Here's the real movie!" I just couldn't believe what I had just seen. It was like the death of cinema. Never experienced anything on the same level before or since, but I will say I've experienced something at least akin to it, still with that stomach-dropping, out-of-body experience, twice more...
2) 2009 - Transformers: Revenge of the Fallen - When the mom eats the pot brownie and we spend like two minutes of precious screentime watching her run around campus for no reason. The whole Transformers series is full of crap like this, but this is the worst, most time-consuming one.
3) 2015 - Star Wars: The Force Awakens - To be fair, this moment wasn't actually watching the movie, it was when the poster came out, and I saw that the antagonist of the film would be ANOTHER Death Star. Yeah, that was definitely the third stomach-dropping moment.
Other than that, I've got a couple more that are pretty high up there.
4) 2019 - Captain Marvel - When multiple alien races come to Earth because there may be a lightspeed engine invented there.....Wait, what? I must have missed something. That can't be the plot! No, seriously, what did I miss? I'm willing to erase this one from the list if there's an aspect of this I just didn't get.
5) 2021 - Spider-Man: No Way Home - Multiple villains come to 616 in the moments before their deaths. Peter decides he can't send them back to those moments before their deaths just to have them die, so he decides instead to cure them...then send them back to the moments of their deaths. That's the plot of the film. It's why I'm not as gaga over this film as everyone else seems to be, and consider it the second-worst of the MCU.
Also, a friend of mine always lists one of his as The Last Airbender (2010) - "They make a prison for Earth-Benders with a dirt floor!"
Okay, now fight...I mean, give me yours!