My idiot seventh grade science teacher, and I remember this because it was so ridiculous.
We had to watch a video on wildlife or something and then write a short paper afterward about what we watched. I was in advanced reading classes when I was younger and read my thesaurus and encyclopedias for funsies, so I had a slightly better grasp of English than my classmates. I'm not trying to brag, but this is relevant information.
This asshat teacher knocked twenty points off my paper because I "did not use grade-appropriate language." I got a lower mark because I was using words she felt were beyond my grade level. I'm still salty about it 25+ years later.