Reviewer's comments should ideally be constructive. They should not just point out the flaws but ideally, it could also provide some suggestions or briefly comment about how to fix these flaws or improve the paper. Reviews should discuss strengths and weaknesses of a paper objectively.

What is a negative comment? It could be just rude or harsh comments as pointed out in the question. An author could also perceive as negative some suggestions that requires to rewrite or delete content in the paper, or that criticize any decisions made by the researchers (weak litterature review, poor experimental design, etc.). Also, if a paper is very weak, a very negative comment could be to not publish the paper because it has no scientific value. Basically, what is perceived as negative by an author is subjective and could be any comment that criticize the paper or requires to change it/reject it or shorten it, and any comment that is harsh, rude or not written in a constructive way.

Reviewer's comments should ideally be constructive. They should not just point out the flaws but ideally, it could also provide some suggestions or briefly comment about how to fix these flaws or improve the paper. Reviews should discuss strengths and weaknesses of a paper objectively.

What is a negative comment? It could be just rude or harsh comments as pointed out in the question. An author could also perceive as negative some suggestions that requires to rewrite or delete content in the paper, or that criticize any decisions made by the researchers (weak litterature review, poor experimental design, etc.). Also, if a paper is very weak, a very negative comment could be to not publish the paper because it has no scientific value. Basically, what is perceived as negative by an author is subjective and could be any comment that criticize the paper or requires to change it/reject it or shorten it, and any comment that is harsh, rude or not written in a constructive way.

Reviewer's comments should ideally be constructive. It should not just point out the flaws but ideally, it could also provide some suggestions or briefly comment about how to fix these flaws.

What is a negative comment? It could be just rude or harsh comments as pointed out in the question. An author could also perceive as negative some suggestions that requires to rewrite or delete content in the paper, or that criticize any decisions made by the researchers (weak litterature review, poor experimental design, etc.). Also, if a paper is very weak, a very negative comment could be to not publish the paper because it has no scientific value. Basically, what is perceived as negative by an author is subjective and could be any comment that criticize the paper or requires to change it/reject it or shorten it.

Reviewer's comments should ideally be constructive. They should not just point out the flaws but ideally, it could also provide some suggestions or briefly comment about how to fix these flaws or improve the paper. Reviews should discuss strengths and weaknesses of a paper objectively.

What is a negative comment? It could be just rude or harsh comments as pointed out in the question. An author could also perceive as negative some suggestions that requires to rewrite or delete content in the paper, or that criticize any decisions made by the researchers (weak litterature review, poor experimental design, etc.). Also, if a paper is very weak, a very negative comment could be to not publish the paper because it has no scientific value. Basically, what is perceived as negative by an author is subjective and could be any comment that criticize the paper or requires to change it/reject it or shorten it, and any comment that is harsh, rude or not written in a constructive way.