Can be anything, from characters not using objects they have on them, to physics not being realistic, or a very big plot hole.
As an example, one of my friends told me that his pet peeve is that in a lot of sci-fi movies, when spaceships run out of fuel, they stop moving, while inertia and lack of atmosphere should keep them in motion.
Generally speaking: Things that humans would never survive. Like, if someone is thrown so hard against a wall that they go through it, they’re not going to live (this happens with non-super characters). Or when someone is falling from a great height and they grab hold of something to catch themselves. Yeah… No.
Or in scenes where fire is present… People having a discussion without coughing their brains out, being able to see, and easily keeping their eyes open, just a few feet from raging flames.
After experiencing any and all of these things the characters will just continue in the story and be able to move and breathe like nothing happened. Sometimes they’ll move with a limp or cough occasionally but this is usually right before they make a 100m dash in record time.