YouTube's stance on bullying and harassment
This can include hurtful language which targets an individual or group of people, trolling, spreading rumours and excluding people from online communities. In the case of harassment, the behaviour is repeated and intended to cause distress. Repeated harassment should be reported to the police.
In cases where harassment crosses the line into a malicious attack, it can be reported to YouTube, and the content will be removed. In other cases, users may be mildly annoying or petty and should be ignored.