My English teacher has horrible spelling, and sometimes doesn't use apostrophes, and since I sit in the front row, I usually point it out, obviously not in a rude way though. The first time I pointed out her mistake, and politely corrected her, she announced to the class that even though she's an English teacher, she hasn't read every book, nor does she know how to spell every word. By now, she's used to my OCD-likeness, and usually, she allows me to just stand up, correct it with a different marker, and sit back down (I sit in the front row, and she usually leans on the SMARTcart, which is about 5 feet behind me, so it's not a disturbance whenever I do this).
UGH! I hate this. My social studies teacher is horrible for spelling mistakes. He just doesn't know how to spell and his writing is near illegible.