I was a bit of a swot, knew what I was doing, and no amount of protestations that I did it to sound more realistic made any difference
You were right- your teacher was a knob.
I sympathize with the pedants…
I had a teacher 30 years ago, and was asked to write a historical account of a day in the life of a cowboy/old Western/Cowboy goings on….
I put loads of effort into this. I wrote it in the style of an olde worlde mid-western, and mis-spelled it it to sound like an authentic cowboy.
When it was marked, I was taken through it step by step, by my pedantic tutor, and informed of my grammatical errors- which were actually not as bad as I had feared.
I didn’t have the confidence at the time to explain that my mis-spellings were intentional.
He would not believe it was written in an authentic style intentionally, but chose to believe I did not have a full grasp of English.
This really bothered me for years, and felt like a true injustice.