I once had a student who scolded me, "Shut up lah, chee bye!" He was in Sec 3 and I was bringing him to see the Discipline Master for reasons which I cannot remember.
Years later, I met him in the medical centre of army camp. I was on reservist and had gone to report sick. I recognised him at once. He was a sergeant who had signed on with the Singapore Armed Forces.
He was courteous and we had a nice conversation.
Whenever teachers are angry with a student, it would help if they remember that they are just angry with the teenage version of a person. The teenage version will eventually grow up some day.