1. Reviews are text. The person writing them may not be meaning to be mean-spirited. We may be taking it that way because our writing is so personal to us.
Text, by nature, is impersonal and easily misinterpreted. Even with the addition of multiple emoticons and colors and several other things to doctor it up and pretty it up, it can still be very easily misunderstood and misinterpreted.

Suggestion: If it is reading as mean, set it aside for a day or two, and read it again. OR, have a friend read it, and then have them interpret it in their words. See if they can find the constructive criticism from it. As the item being reviewed isn't as personal to them, since it is not theirs, they will be able to view it with fresh and different eyes.

Exception: Don't make it your best friend, your spouse, or someone deeply protective of you. They might take it the exact same way you do.

2. Some people are mean and rude.
Some people don't mean to help anyone out at all. They just wish to be rude, and to hurt others. If you happen to run across them, this is what you do.

Suggestion: The first time you get something from them, ignore them. If they are obviously just trying to be mean, they obviously aren't worth your time. Don't respond to them, because it will only start an email war - you are actually feeding right into what they want. They threw the first punch, you responded in kind, and therefore the war is justified. Don't engage.
The second time, block them, and report them. Likely, if they are doing it to you, they are doing it to others. Mean people are mean, and it is rarely isolated.

3. Reviews are suggestions. You are under no obligation to change your item the ways they mention.
If you don't agree with what they have to say, you do not have to change what they want you to. Find the things you do agree with - rarely does a review arrive that doesn't have a good suggestion to it. The things you don't agree with, don't change. No harm, no foul.

4. Don't forget to thank the reviewer.
Unless they are truly just horribly rude, don't forget to thank them. Even if you don't take any of their suggestions, they did take their time to give you their opinion. Not everyone does. (No need to elaborate on what you did and didn't change, either. It isn't needed. Or to tell them they are wrong about some of their changes. Just thank them for taking their time to stop by your portfolio and give you some feedback.) It is appreciated, and it encourages them to do more. It shows them that their time was appreciated. Even if you didn't exactly agree with them.

5. If you feel so inclined, pay it forward.
Some of the best ways that reviewers learn how to review is to receive reviews. If their review hurt your feelings, you could consider showing them how they could do a better job by picking one of their items and giving them a review (one that wouldn't hurt someone's feelings). Show them how you would do it. They might learn a trick from you. They might not, but you never know. Can't hurt to try.