This was an awesome motivation on how to handle with people like these. I didn’t have a troll yet in the comment section of my videos but I did notice the one you were dealing with.
I guess just keep downvoting and not replying to what they are saying might be the best solution. After some time they will lose interest and leave again. Just like this one. I have just checked his profile. Hasn’t been active anymore for the last few days ;)