Many teachers use dry humour as a way of getting their point across to students.  This is bullying as it tells the kids they are not respected and that other kids are allowed to speak to them in the same way.  I was one of those kids that teachers bullied.  No throwing of desks or chalk like I have known other teachers to do during my time as a teacher.  Just using sarcasm and nicknames and mockery that brings out laughter among the peers and ensures that the student will be mocked as soon as class lets out.  Teachers and parents be careful how you speak with your children.