Can I demand re-submission of a manuscript that has an odd document layout? I am assigned to review a paper that has an extremely strange page layout (the pages are squares, single column with about 150 characters per line), making it very impractical to print or read. It is for a journal and was submitted via Manuscript Central.
I could of course read it on my screen (which I don’t like at all), or print it with either rotating or stretching the pages (which I tried but it’s very awkward to read and therefore extremely distracting).

Is it okay to write to the ADM and ask them to demand a re-submission in a proper document layout, i.e., A4 or US Letter? Or am I being fussy?
No. It is not your job as a reviewer to demand things. You can inform the editor that given the format of the manuscript that you will not review it. The editor will then likely look at the manuscript and either decide that you are being a pain and find a new reviewer or that the manuscript format is ridiculous. In that case, they will apologize to you and tell you that they are requesting a reformatted version.

Unless the format is really awful (like less than 10 lines a page or greater than 100 characters per line), the editor will probably conclude you are a pain.