A few more, then I'll let someone else jump in. Having read the OP, I am reassured to see that this thread is meant to be about teacherisms that we remember.
One afternoon a week, I and a few other children were taken to another classroom and made to do exercises such as skipping, forward rolls, hopping, throwing and catching beanbags. I thought this was quite fun at the time, but I found out some years later that it was a group for children who "needed extra help with gross control and co-ordination".
When we learned about Victorian objects, the fearsome headmistress whom I've mentioned a few times demonstrated ironing, using a flat iron which had to be heated on the stove. She wore a maid's outfit for this (teacher took photos with a polaroid camera), and most memorably of all, demonstrated how to check the iron was hot enough: by spitting on it!
A much feared teacher once walked into another teacher's story time, made a beeline for one child, and said, her voice rising to a crescendo: "What do you think you're doing, you horrid little boy? Go and stand on one of Mrs Smith's tables!" A stunned silence fell, including from Mrs Smith. I don't know what the boy was doing to warrant this humiliation, probably just talking.
The same teacher once gave us a lesson on handwriting practice, and wrote the word "kitten" on the board; more the half the class copied it into their books. She then did a slow march around the classroom, tossing children's books on the floor. She then made them pick their books up, and stand at the front holding them up. These children had committed the crime of writing "kitten" when she hadn't told them to. After she had sent these wretches back to their seats, she said in a kinder voice to everyone else "and now write the word 'kitten'."
Also this discussion, which I swear really happened, and I'm not making it up:
Boy (a bit of a troublemaker, coming out of the toilet, pointing to another boy, but not seeming that bothered): He weed on me!
Teacher: (unmoved) Oh dear. (To the headmistress, who was passing) Well, I don't think we'll let him go to the toilet again.
Headmistress: Of course not. And he can write about it.
Teacher: Should he do it in his book?
Headmistress: Oh no, give him a piece of paper. And if he wets himself, too bad.
I don't know how serious they were being; I was then imagining this lad having to write "I weed on John". I expect the headmistress didn't want it in his exercise book for parents to see.