this is something everyone has known since the dawn of the office environment

As long as you're just sitting in the back and you're not supposed to attend any kind of formal meetings or anything like that, in the heat we've been having the last few days I would have assumed it was okay to come to the office in shorts too!

Social rules are often arbitrary at best & classist at worst. I'd struggle not to laugh in their snooty faces.

shorts have never been appropriate office attire since the dawn of desk jobs

It depends on the office's dress code and if it's a special day or not (important clients, board meeting, etc.). I've worked in several offices where shorts were definitely fine.

I don't agree with the rules but most offices have a "business casual" dress code and, sorry to say, shorts are definitely not appropriate. It sucks, especially if you don't have a front-facing job where you have to interact with customers/clients, but that's how it goes sometimes.

unless you work at Google, it's never proper work attire. not even casual Fridays

Always verify dress codes before wearing something to work. Most offices don't allow shorts, so not sure why you wore them to begin with.