Constructive criticism has never hurt me. It's frustrated me when I felt the person wasn't trying to understand, and then I became better and realized they were right.
What has hurt me is criticism from people I trusted to genuinely care and help me. Not the criticism itself but the way the criticism was completely off-base and could have been clarified if they had honestly read the story up to that point.
Case in point: I had a "friend" who offered to do some editing for me. I mostly wanted input and the fact she was as demanding about grammar as me helped. By Chapter 6, she was complaining that I was demeaning toward the female protagonist. I asked how. She said it's in the way the male protagonist keeps addressing her, his pet name for her.
It kind of took me by surprise because, well, the pet name was an important element to the story and explained in the Prologue. There is nothing demeaning about it in any way.
I mentioned the Prologue and asked if she had read it (If you're editing something, shouldn't you be reading everything?). She assured me she did and then continued on with a rant about how such a nickname is demeaning toward women.
I took a deep breath and tried not to take it personally. I even tried to reason with her and replied with, "Well, he isn't an actual black butterfly, either, but that's her nickname for him." I tried to laugh it off to keep the peace between us. She said there was nothing wrong with that but for him to be referring to his "little crane" made it sound like he was a predator of children.
I bit my tongue and pretended not to get that text.
A few days later, she messages me that she finally reached the first romance scene. She was "unimpressed." I said, "This isn't an erotica and it was their first time." She said, "Well, you say it's a drama and a romance novel, so it's supposed to be assumed that there's going to be smut. Not only did I have to wait until Chapter 13, but I was left unsatisfied."
Needless to say, she ceased being an editor (I was even willing to pay her $500 just for reading and giving basic feedback).
I think the "hurtful" part comes in learning someone you trust to be honest and take your work seriously doesn't really read your work and then uses you for some cheap thrill and a quick payout.