Theory:

Flaming: When two or more people fight online over any issue, using vulgar and foul language, thereby degrading one another.
 
Hacking: Using a person's device by logging in to his/her account and accessing it without permission. It is similar to breaking into someone's house without permission.
 
Cyber stalkingFollowing someone without their knowledge, looking at their pictures, monitoring their activities like where they live, which school they go to, what time they sleep etc.
 
DenigrationSending unnecessary information, secrets about someone online, with the purpose of damaging their reputation.
 
Impersonation: Breaking into someone's account and chatting, posing as that person to his/her friends by assuming their identity. Then person's friends or relatives may not know that it is someone else and may get a bad impression.