I am from a country where humor is a part of the culture, and I recently prepared the following referee report:
The manuscript solves an interesting problem, but, unfortunately, the authors are a bit late with their study. The very same problem and the same results were described just half a century ago by XXX, Journal of XXX (1969). Like the manuscript under review, that paper ... <details>
It was a very important problem at the time, but the research field of XXX has somewhat evolved since then, so I'd like to take this opportunity to encourage the authors to catch up with the recent progress and do something on the cutting edge of research.
The idea was to use a humorously gentle style to jokingly portray the authors as stuck in the old era, especially given that they are now professors in their 60s or 70s. "Just" half a century is a huge time period, and the research field has evolved beyond what people could even imagine back then.
To clarify, the problem solved in the manuscript isn't something everyone in this research field knows about. I myself didn't know about that problem when I received the manuscript for review. However, I checked the literature and found that paper in about 20 minutes. The paper is highly cited and was helpful in solving various problems when the fundamentals of the research field were laid. It looks like the professors made an attempt to do something fundamental and failed to properly check the literature first.
Considering the authors and the editor are not from my country and might find such a style inappropriate or even offending, I rewrote the report in a rather boring manner with a bit of empathy:
The manuscript solves an interesting problem, but, unfortunately, this problem has already been solved in the literature. <details>
On the bright side, I can confirm that the authors' solution and conclusions are correct. I would be happy to recommend this manuscript for publication if the problem had not already been solved.
I sent the latter version and now feel that I may have played it too safe. My original report could have made a day for the editor and convincingly taught the professors an important lesson. I feel very tempted to use my original style in similar circumstances in the future.
My question is addressed to people who have worked on editorial boards. Are reports like my original version acceptable? What are the policies and practices regarding this? As an editor, what would you do upon receiving such a referee report?
P.S. I don't want to specify my country, because I don't want to start a discussion about its culture and people. My question is about humor in referee reports.
Please don't be too hard on me if my original version is highly inappropriate. After all, I didn't send it. I'm asking this question to ensure I won't do anything wrong in the future.