Why are some teachers so emotionally abusive?

Question

I was always a polite student. Yet these lecturers will only be polite half the time. The other half they would literally shout at me for no reason. It's as if they were either bored of me and therefore become rude/ emotionally abusive or they were having a bad day and taking it out on me both are not valid reasons to mistreat anyone, student or colleague. There could have been more reasons but me being rude/ impolite was not one of them.

Update:

@THE BANNIBAL ONE, it's okay to be different if you're for example of a different race, religion, culture, into different hobbies but when you're different because you're a jerk- that's not okay. That's bad behaviour and shouldn't be acceptable.

Answer 1

They hate themselves and what they did with their life. Take it out on students.

Answer 2

They must have had a bad day.

Or that is how they are.

Everyone is different.