The most common occurrence of this is as a kid: perhaps you misplaced your pencil or it rolled to the floor while you were preoccupied. The first feeling is that one of your classmates must've grabbed it.
This seems to bleed into adulthood for some folks as well, a knee jerk response to irrationally attribute a problem to a nearby human they don't like.
Is there a noun or adjective to describe this? Hopefully one that is pejorative in nature, but that's definitely not requisite.