I am reviewing an article for a journal and I am going to recommend against its publication. In spite of that, having been on the receiving end, recently, of a blind peer review report that was completely off-base as well as just nasty, and having been made aware of the pitfalls of reviewers trying to use the process to force their own agendas onto other scholars in ways that I don't consider appropriate, I am trying to parlay these experiences into writing a better review.
The process has definitely given me an appreciation for how easy it is to inadvertently fall into ad-hominem attacks against the author of the article, even if that isn't really what you mean to say.
So for example, where I had originally written, without really thinking about it:
"The author does not appear to have a comprehensive grasp on the panorama of [area of my subfield redacted to protect the innocent]."
I changed the text of my report to read:
"The article does not reflect a comprehensive picture of the breadth and variety of [redacted things in this area of my subfield]."
It's still critical and it's still, honestly, quite harsh. However, I'm not insulting the author by suggesting that s/he doesn't know the material; just that his/her knowledge, which I assume to exist by virtue of the fact that s/he is at the stage of submitting articles to peer-reviewed journals, is not reflected in this particular presentation of the material.
When I have received critiques of my work, I have found the detailed, critical, harsh ones that engage deeply and in detail with the work itself to be incredibly valuable; and I keep going back to them over and over again as I revise. But I find myself tuning out the ones that resort to ad hominem criticism. Even if it is an understandable rhetorical misstep on reviewers' parts, I think it's just a better use of everyone's time and intellectual resources to make a real effort to present critiques of work in ways that do not put their recipients on the defensive.