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.
These are more common in tv than film but happen in both:
Any time a shot is given with a syringe, especially by an addict, it’s almost always done in a way that would severely damage the person.
And more of a narrative issue that is common, but I hate the trope where a person overhears part of a conversation and jumps to conclusions, but had they listened for a few seconds longer it would have contradicted their conclusions.
https://tvtropes.org/pmwiki/pmwiki.php/Main/OutOfContextEavesdropping