This type of bullying is much more recurrent because it’s verbal abuse. Verbal bullying can range from insults to threats, the mockeries, the derogatory words, to teasing about the sexual condition of the person, about his physical features, about any imperfections she might have, about one of her tics, or even about her skin color or it’s origin. The person who suffers from these mockeries and sees her self-esteem undermined.
The answer to "Why do you humiliate, insult and harass this person in your class ? » is usually "I don’t know" or "it was a joke".
During teenage years, dealing with this type of comment makes us much more complicated, because we are going through a phase where our sensitivity is acute. This is why it’s very important to cut short this problem. Many people who have had verbal bullying have had to increase their self-esteem and believe in themselves at the cost of many efforts.