When I was working for that large ISP's tech support department, it
was a strictly telephone job.
That was fair enough; a good half of the problems were people not
being able to get on-line at all (this was after all in 1998), and
sending a letter would have been too slow. But we were definitely
never supposed to be seen by the public.
And therefore there was no reason other than managerial whim for the
dress code, which was "either shirt with collar and tie, or company
sweatshirt". And you could only get the company sweatshirt after you'd
been there three months.
I hadn't heard of malicious compliance in those days, but that was
what effectively I did: I scoured charity shops for the loudest ties I
could find. Nobody on the job had time to look at anyone else anyway,
but the supervisors winced every time they walked through that part of
the room.
I still have many of them.
In the last week (before I moved over to Network Operations, which was
better paid, more interesting, and much closer to home) I used a strip
of chainmail that a friend had found surplus to requirements for the
hauberk he was making. Yes, one can (or I could, with a bit of
practice) knot this into a half Windsor. It was heavy, but thoroughly
worth it.