Watchtower-Free:
I went to a district assembly several years ago on a Sunday. I wore a denim skirt but was otherwise well-attired (at least I thought so). Well, during the lunch break when I was walking outside along the grounds and looking for people I knew, I became aware that I was being followed around by some "brother".
I later found out that they follow people wearing denim because they think you are there to make trouble or place apostate literature.
In my opinion, I think the religion's hatred of denim and making sure that JWs look "businesslike" is to give the impression to the world that they are "educated". Meanwhile, nothing could be further from the truth.