In 8th grade, my best friend and I skipped one class. Right before we left, we saw one of our teachers in the hall, apparently he saw us too. The way he treated us for the rest of the school year was annoying as hell. Suddenly he turned stonecold whenever he addressed us in any way, made sure to always picked one of us of to answer his questions that were actually aimed at the whole class, gave us one bad grade after another without any explanation or feedback. After having mostly A's and B's in his class before (we've had the same teacher in that class since 5th grade), we almost failed by the end of the year and we couldn't understand why. We were too terrified to ask him but we realized it must've been because he saw us skipping class. And the best part, we skipped gym class, he was our German teacher. I hope he reads this: It wasn't even your class, why were you so salty Mr. E? You gave me nightmares to go to school for the whole damn year and I'll never forgive you.

TL;DR I skipped gym class once, my German teacher caught me and remained pissed at me, making sure I regret my behavior for the rest of the year.