I have three ways of dealing with troll comments and each tactic depends on your niche.
1. First technique is the obvious hide user from channel / block / ignore. I do this on channels in a positivity niche etc.
2. My second technique usually my teaching educational niche channel I'll reply to everyone including the trolls. I'll be a little sarcastic and Witty but always ending with "thanks for watching" kind of like a kill em with kindness approach as someone else mentioned.
And last technique...take this with a grain of salt. To me personally, some people may not like this technique because they will say you are not presenting yourself professionally but there are some who will be on your side. In other words, it's relative and you can't please everyone.
Anyways...
3. This technique probably won't work in a positivity niche. I use this technique on my "eerie facts" channel so it's kind of fitting. However, try to strike a nerve and get the troll to argue with you because at the end of the day thats all they want is attention.
By going back and forth with them it sparks the engagement up on your video. I had "argued" with a troll on a video and that channel usually gets 200-300 views on average. That specific video before I replied to the troll was at 367 views by the next day it was at 5k views...
like I said some won't agree with this and some might think it's straight up wrong to do so but for me, it's your channel you do whatever you like. You can't please everyone and nowadays everyone has something to say...
I am just sharing with you what I personally do on my channels. As I mentioned everything is all relative so if it makes sense to you go and do it.
Those are three different strategies you can take into consideration.
Now if someone replies to this trying to troll me about these techniques then just know this isn't my thread so I'm not here to boost it so you'll probably get ignored.
I got multiple channels to attend to so good luck!