I don't like dealing with people like that, though sometimes the delivery of said concrit isn't exactly the most tactful either. With some people, you can get away with going, "Look, I don't like this, this, this or this and here's my reasons why." and with others you have to go, "I loved this, I thought that was good, but I feel like such and such needs more work - perhaps you could *insert suggestions here*"

Sadly, I think whatever skills I have for dealing with touchy authors I learned from flamefests with Mary Sues in my RPGs and trying to talk some people down from the ledges of quitting.