Imagine you're lost in a good story, immersed in the characters and setting and plot, and all of a sudden you trip over something that doesn't belong, or that doesn't feel quite right, and then, unhappily, you're back in the real world. It's like a glitch in the matrix, and it makes you feel a little squeemish inside.
These glitches can come in many shapes and forms: inconsistent characterisation, time lines that don't match up, unrealistic dialogue. Or it could just be a word.
I read a series a few years ago (which I loved for the most part) that actually gave me an uncomfortable squicky feeling every time I read a particular word. The word was 'boyo'. My aversion is not to the word itself, but to the author's use of it. If one particular character, or characters from a similar area, used the word in speech it would be a characterisation tool. Something to mark them as different. But the word wasn't used that way. It sat where every instance of 'man' or 'boy' should have been. And the book wasn't even in first person! I started pausing every time I read 'boyo' and replacing it with 'man' or 'boy' in my head, so annoying was it. I almost stopped reading, even though I enjoyed the rest of the book.
So there you go, one simple way to throw your readers out of the story.
What have you read recently that's made you pause and pull back from the story? Or does this sort of thing not bother you? If you're a writer, do you have a word you like to use that others might find out of place? If so, it could be time to use Word's find and replace tool.