I think that how much this has blown up, is a bit worrisome. All of this.. over a butt..?
It's making someone's decision to do something seem like such a bad and horrible thing that they themselves begin to question the validity of it. It's a rather unfortunate yet very effective form of control(for most people), and an easy way to point out narcissists, as it's part of their way of breaking someone's mind down.
Like let's say you decided to die your hair red, even though I said not to, because I liked it black. I will keep on bringing this up and over-exaggerating how it stupid it was that you died your hair, and will not let it go.
Short definition: You begin to doubt your own thinking.