Don't be a Troll.... Some people really take it seriously.
Hitler got rejected by Academy of Fine Arts Vienna twice. If he got accepted, and become an artist, things might be a lot different...
Being an artist is very different from other hobby or occupation. Professional or not, every time we create a piece of art work we put a little bit of ourselves in it. So it is no way that we don't take it personal. This is who we are, and we put it out there for the world to see. So saying "your art sucks" pretty much equals to "you suck!"
So next time when you criticizing other people's work, try to keep this in mind. Constructive criticism is always appreciated, but there's no need to be mean about it. You can be constructive and be encouraging at the same time.