Dear god, I remember a day near the end of my last school year (6th grade, in 7th now) where we had a substitute teacher who didn't care about what the students did.
All hell broke loose.
Kids were yelling like they were partying, you'd have to be lucky not to see things being thrown around, many students stood up and I EVEN SAW TWO CHASING EACH OTHER IN THE CLASSROOM. Thankfully, my school lets you go outside for lunch so you can avoid the school's lunch if you hate it. However, I just went straight back home and decided to skip the rest of the day.