(for the acronymically challenged among you, that's "In My Very Humble Opinion")
Highly irritating -- someone not liking a movie, a book, a song, whatever, because it doesn't correspond with their point of view, their experience, or their perspective, and their PoV, experience or perspective is the Ultimate and Only one available. In a nut shell "It just doesn't happen that way and I know because I'm from there and it didn't happen for me." This isn't saying "I don't like it." This is saying "I don't like it because it's wrong and I'm right."
I'm highly skeptical of any opinion that reduces down to that equation. No one has the entirety of human experience sown up for handy reference. Saying "no one would do that" when you mean "no one I know would do that" or "I would never do that" is, shall we say, not the most intelligent way to present one's opinion. There isn't much that someone, somewhere, in some situation, hasn't done.
She's right: someone, somewhere, has probably done whatever it is that you don't/can't buy into.
My favorite example is (SPOILER ALERT!) the ending to Wharton's Ethan Frome, where the "hero" tries to commit suicide by tabogganing into a tree. Sorry, I just do not buy it. The odds against it working are astronomical - and, true to life, in the book, it does not work. An English teacher at MPOW posited that we react and respond to fictional situations positively if we can suspend our belief enough to buy into the premise.
I can buy into the world C.S. Lewis creates in Perelandra more easily than I can buy into someone trying suicide-by-taboggan. Why? Because my experience with sledding/tabogganing says that it's a flawed premise, while I have no experience on a water-based unfallen planet that would contradict Lewis' tale.
I have to concur with Sherri's statement. It's just that I (and most people) are so egocentric that we prefer to use ourselves as the Gold Standard when reviewing a book or movie or play or whatever, and so we do say "no one would _____" or "no one could possibly _____", because in our world, no one could.
Just my VHO.