You have every right to use YouTube without fear of being subjected to bullying or harassment. Bullying can be reported and action taken when things cross a line. To flag a video you think is inappropriate (Click on the little flag bottom right of the video) and YouTube will take a look at it to see whether it breaks their terms of use. If it does then they will remove it. YouTube rules say cant upload videos with hate content, nudity or graphic violence and if you find one on someone else's space. click on the video to flag it as inappropriate. If under comments, you are being bulled, harassed or threats are being made, they have a reporting tool page where you can report the bullying and they will investigate.
Useful pointers Simon. It is crucial to familiarise ourselves with all the tools on YouTube?
Is YouTube more prone to bullying than other social media platforms?