I walked out once, teacher was trying to do some serious bullshit involving pretty much the entire classes' projects and how they were formatted, which for some reason counted as around 40% of the project and the project was around 20% of our grade. I stood up and said, "Fuck this."
Then proceeded to get my things and walk out. I do believe a few other people followed me, but I didn't care at that point. I just went and chilled in my next period's classroom. Incidentally, nothing ever came of that. I think the point got across to the teacher, but they never did change anything. I went from having an A to barely having a B.
I think at that point it was the end of the year, and the teacher didn't want to have to answer as to why I did what I did, because she probably would've gotten in as much trouble as I would have. At least that is what I like to think.