I worked in that world for 34 years. In theory, there was no dress code at all, though I was able to disprove that. Occasionally I showed up to work wearing a suit and tie for no reason other than to rattle people's nerves. Clearly I was breaking the unwritten code.

Speaking of tolerating weird behavior of valuable employees, I have a great anecdote. I worked at Bell Labs, a highly regarded research and development organization which produced a record number of innovations. At the time, it was a division of AT&T, and that the same time, AT&T was a much bigger company than it was. There were a couple of guys who, after lunch, would play games in the corridor by throwing and rolling quarters down the hall. One of the high ranking administrators saw this and said we have to put a stop to this. But someone informed him that these two guys had come up with an innovation that had saved the company 5 Billion dollars with a 'B'. You should not discourage people like this. The big guy relented, and the games continued.