Some teachers shouldn't be allowed to be teachers.I did exactly the same sort of thing a few times, but as for anyone trying to sabotage my work, they all did that sort of thing all the time anyway so it made no difference to me. The most memorable was my year 10 maths teacher. I always finished any problems immediately than I'd sit there quietly reading a book.
The teacher didn't like that, he said it wasn't fair that I could sit there having a bludge while everyone one else had to work. That entire attitude doesn't sit well with me even today, and when people try that one on me I arc up big time.
"You have the cheek to start picking on me when I've done my work. Meanwhile the rest of these (very derogatory Aussie term) are still counting on their fingers and can't tell you their 6 times tables. You're wasting my time and theirs.". And I walked out. That was the last time I went to maths class that year.
The good ones that I still smile when I remember them, some 40 years later, are the ones who actually encouraged us. They spent time trying to make sure each kid in the classroom had understood what they were learning, and they also encouraged talents.