Okay, I'm gonna share my experiences too, I read everyone's and I relate with most of them.
So, the first story, takes like around 5 years ago, I was doing a doujinshi called "Pokemon Brilliant", a series with my own pokemon region, new charas and I made characters from the oficial manga Pokemon Special appear in my comic. For that time in the forums, people loved it... later. Because when I first uploaded the chapter 1, I got like a TESTAMENT of a person that said everything wrong with my comic, pointing all my mistakes in drawing and comic composition, so I replied gently to her "well, it's not that terrible, I can fix it in the next chapters", I did and the person never said anything... actually she never commented ever again in my thread. In other place where I was uploading it, a person appeared saying that I had problems with the story composition and that HE WANTED TO HELP ME, I inmediately guessed something was wrong, and I rejected it but gently, because I'm in my right to not want to receive help and want to instead fix it in my own, I said thanks for the consideration but I work alone. What happened later? the person kept spamming me with private messages about how much of a terrible person I was because I rejected him, oh and he did all of these messages putting a picture of Catmon from Digimon, I replied to him to please to stop messaging me and to leave me alone (I never insulted him or anything). Later because of issues with college, I cancelled the comic leaving it with 12 chapters. Then the person sent me a message again saying (And I still remember his words) "I'm glad you stopped drawing that comic, though, I WISH YOU COULD HAVE DIED INSTEAD!"
and I replied to him "if you wish to someone to die just because you got rejected, then boy, you have a serious problem."
If someone ask, I reported him to the admins, tons of times, but after I replied to him, he stopped replying.
And now the most recent thing, around a year, was when I was working on my actual comic Final Light, I had the idea to work with someone very special to me, it was like crossover with his comic and mine at some point both stories would meet. But this person all the ideas I had for MY story, he said like "that idea is stupid", "you don't know how to develop characters, that's why they are all bad", "this part of the story is stupid", "My story is so much better because is SO f*cked up, but yours yeah, is just hardcore", and for that time I was really depressed and even today I still have doubts of my comic if it's good or not. Later for things with destiny, we got a big fight and we stopped talking to each other for a year. But I know this person is still going to my profile in DeviantArt just to make fun of my art and is expecting me to upload Final Light just to, again, make fun of it.
But I decided to re-take all the ideas I had that he called them stupid and use them, though, I'm still preparing myself if he ever decides to send a hate message to my facebook, or gmail, or dA too (since he can make tons of fake accounts)
Though, I should say I'm kinda used to hate xD for some reason I get either very loved or very hated. But these experiences will help me in the future if it happens again.