So aside from poorly timed jokes:
Iron Man - Coulson saying that they decided to try out the name "S.H.I.E.L.D.". Yes, it was retconned later, but just the fact that an intelligence agency would not have immediately realized their organization's name had that acronym is just studio pandering.
Thor - Dutch Angles but also the shouting moments from Hemsworth, Hiddleston, and Hopkins just feel so cringy to me.
The Avengers - "I have a plan. Attack."
Iron Man 3 - Killian not dying when the Mark 42 was blown up. Made perfect thematic sense, and the unnecessary Super-Pepper scene just took me right out of it.
Avengers: Age of Ultron - "I think you're being hard on yourself." "Here I was thinking that was your job." is the rock bottom of this plotline.
Black Panther - "WHAT ARE THOOOOOOOOSE??"
Avengers: Infinity War / Endgame - The 1 in 4,000,605 thing really annoyed me. Like all that made me do is look for plot holes.
Ant-Man and the Wasp - The part where Janet says if they fail, it will be a century before they can find her again. Just like Infinity War, these stakes are unnecessary.
Spider-Man: Far From Home - The part where Peter calls a drone on Brad just felt silly.
WandaVision - The Bohner scene added absolutely nothing to the series, and this is from someone who didn't want him to be the Fox Quicksilver.
The Falcon and the Winter Soldier - The only part about Walker's arc that bugged me was the joking with Bucky. I can buy you still working with them for a greater purpose, but these guys do not like each other at all. The Zemo mask was pure fan service too.
Loki - Not a fan of the acting/dialogue during the Alioth scene.
Black Widow - Why did we need the pheromone lock? What did that change?
Shang-Chi and the Legend of the Ten Rings - Trevor understanding Morris fluently was just a bit too unbelievable for me.
Eternals - The sex scene felt completely shoehorned in.