I've told this person (who IS actually a friend I know in real life) countless times that they've made some remarks that step over the line for me, but he persists in making them anyway. Some of the time, they're valid points, but he says them as though he's trying to be funny and it makes me feel terrible about the work he's commenting on.

For example, on a piece I'd mentioned how pleased I was with, he said " Is he wearing.... cleavage? Why does his chest stick out like that?"
I know that this is because the character featuring in the picture was wearing a very losing jumper and moving in such a way that created folds across his chest. But, when he put it like that, I just felt any pride I had in that picture implode.

On another picture I said I'd been working on for a whole month and that I was ridiculously proud. His comment spawned from the fact that the character was sitting on a wall, and his tail was flopping over the other side of it. But instead of asking what exactly it was, he said-
"is that a crow's foot on his butt?"
THAT hurt.

I know I shouldn't take it to heart so much, but damnit! I've told him time and time again that the way he comments on my stuff upsets me and that he's just plain tactless sometimes, but like I said, the comments keep coming. I can't just block him- he sends floods of little pleading messages to my inbox, begging for forgiveness he doesn't deserve.