I wish I had proof of this but this happened years before I found this place!

I was classmates with an r/iamverysmart who boasted about how he was very good at math, and how he taught himself Calculus so this class (college algebra) was child's play to him and he would definitely get the highest score out of all of us. Well, whatever. We took our first exam and class average was in the high 70s, so there he was in the corner already celebrating thinking he brought the average up. When he gets his paper back, it's a 68%. He got a D, with a plus for effort. He's furious, acting like the professor has it out for him. Storms to the front of the room and tries to contest to the professor that her grading system is botched. The professor, being the good soul she is, takes time to let him explain his reasoning and then allow her to explain why she graded his paper as such. After reviewing every single little mistake he made, he leaves in a childish rage, presumably to impose his calculus-level brain to more sophisticated concepts, like defeat.

And they never saw him again.