This is something that comes up a lot, and it's something that occurs everywhere, not just Youtube. I've got a lot of experience with it as somebody who has been putting my own content out there since I was like, 10.
I'm gonna say to you the same thing I say to everyone. Literally, I'm just gonna copypasta some earlier posts of mine
As someone who grew up as part of the Internet Hate Machine, there will always be assholes, and people who get their kicks by pushing other people into the dirt.
The only thing you can do, what you have to do, is ignore it completely. Report it and move on. Never take it personally, and never give them the satisfaction of acknowledgement.
And to add to that, don't ignore constructive criticism just because it's not a positive comment. But do make sure it's constructive, and not just criticism
They want you to respond, they're trying to bring you down to their level.
If you want to live a public life online you have to grow some thick skin.