He insists that he is the ugliest person in this subreddit, when he is clearly not all that terrible looking when you look at the pictures he's posted.

Depression often does that with self image. A lot of people in this sub feel very strongly about certain aspects of themselves.

He persistently cherry picks any comment that acknowledges he might be slightly below average and uses them to prop up his established narrative of "you all agree I'm a hideous freak. Girls avoid my very presence because of my face, and you all are clearly hypocrites for suggesting that mental issues may be playing more of a role than my unattractiveness". Look at his post history and forgive me for losing my patience a little with someone who's so unwilling to listen.

If you're starting to get worked up, then take a break instead of commenting. Acting like a dick to someone who's clearly struggling a lot will never help. There's always a tactful way to say something, and it's clear that you don't really care about being tactful.