Why would Kant or other deontologists label bullying wrong?

Bullying is abusive social interaction between peers which can include aggression, harassment, and violence. Bullying is typically repetitive and enacted by those who are in a position of power over the victim. A growing body of research illustrates a significant relationship between bullying and emotional intelligence (EI). Mayer et al., (2008) defines the dimensions of overall EI as: "accurately perceiving emotion, using emotions to facilitate thought, understanding emotion, and managing emotion".[74] The concept combines emotional and intellectual processes.[75] Lower emotional intelligence appears to be related to involvement in bullying, as the bully and/or the victim of bullying.

https://en.wikipedia.org/wiki/Bullying#Emotional_intelligence

Distinguishing Bullying from Other Hurtful Behaviors

https://cyberbullying.org/distinguishing-bullying

Bullying is wrong and hurtful

https://www.prevnet.ca/bullying

http://www.togetheragainstbullying.org/tab/understanding-bullying/myths/

It's extremely wrong to the point of it being a criminal act. Anyone who disputes ethics has no moral compass, hasn't studies any Philosophy or ethical sciences.

Bullying is very hurtful to the person being bullied. Any action of cruelty to another person is wrong.

Political correctness.

Don’t know.

You might have set your mind to tolerate when others bully you and may laugh with them bullying yourself. Bullying is wrong. It will lead to unpleasant situations and go up to murder. Finding pleasure by bullying others is a weakness of mind and bad too. People do many mistakes for their own pleasures. They must well understand that each and everything is taken into account and create the consequences.

Your teacher may be trying to bring out the distinction between teleological and deontological ethics, which is the difference between judging based on specific results and judging based on general rules--similar to the difference between inductive and deductive reasoning. Sadly, the use of the word "bullying" manages to combine fallacies of appeal to emotion (misercordia) and circularism. If the rational meaning of "bullying"--tyrannizing--is understood, then the illogical conflation of "circular emotionalism" may be unpacked: the state has a major claim to tyranny (use of force) which is justified on deontological and teleological preferences as to the "good." Thus, a "bully" may be well-served by being incarcerated--"bullied."

A similar example is "It's good to lie to SS if they're asking if you've seen Anne Frank." This scenario involves the deontological power of political correctness vs the teleological and beyond-the-state (deontic notions of Nuremberg political correctness): https://en.wikipedia.org/wiki/Nuremberg_Laws

For the strict deductive deontologist, one may escape such teleological issues by using Kant's Categorical Imperative, which is a) specific, b) informed by all relevant axes or salients, hence c) likely to figure out that bullying or death camping is incorrect for those of one's own values, therefore e.g. it is deontologically correct to lie to said officers of the state if you value Anne Frank's life more than "political correctness."

Thus, if one deems a certain religious group to be dangerously subhuman, it is teleologically correct to dispose of them. So, teleological ethics is a person's values of what is the good, and meets deontological ethics as "it is a general rule not to do bad, but to do good always."

Thus, there are issues for either a Kant or a Mill, as for them Plato's question "What is the Good?" is perspectival, i.e., not based in Noetic awareness of "the Good, God." It does obtain that "God" may have mercy for whom God decides--indicating neither strictly deontic nor strictly teleologic action.

So, basically, "deonts" favor rules, based on what seems right, and "teleos" favor "what seems right, in the situation," preferring not to make over-reaching rules. The value of having rules may be that the rules generally guide actions, helping keep teleos in line; howbeit, governments have given deontic rules for the disposing of politically incorrect groups, e.g. the millions on Chairman Mao's "enemies list."

Your answer can be found here: https://files.eric.ed.gov/fulltext/EJ1139187.pdf Page 160, paragraph 6.

Yes