If it's criticism, I usually leave the comment up and reply to it. If it's mean, but an opinion of someone, I usually leave it alone - other people tend to reply on it, sometimes agreeing, sometimes not agreeing. I think they all can have their opinions, so long as it doesn't get too out of control. If things were to escalate too much in the comment, I'd delete it. If it has too much profanity, I mark it as spam. If the same person were to post mean things on multiple videos, then I think would delete them and block the poster -- this hasn't happened yet, but I'm sure it will eventually. If it's a pervy comment, it goes straight into the trash! I'm a content creator, not an object. >.<