This isn't a thin skin problem.

Mean comments are a waste of space; they take up the space on the page where actually valuable content should be.

I've always hated the "grow a thicker skin" comment, regardless -- it shifts the blame onto the victim, and is simply impossible for some people and some situations -- but the problem here is that one person gets hurt (more or less, depending on thickness of skin), and lots & lots of readers get crap instead of brain food.