What do you think of people who refuse to hear constructive criticism?

You can give him constructive criticism. You can comment only what you find positive. You can also "recommend" that he use spell/grammar check. So going forward just comment on the positive, because I WILL guarantee that a publishing company will just throw it away and most likely not even bother with a rejection letter. Keep the peace.....there are far too many out there that will be too willing to kill his dream of being a writer. This will also be a good lesson for you going forward. People want to hear positive feedback no matter what. When you can deliver negatively news or information positively, then you will have made a great accomplishment.