The dress code in my office (population: 10 grad students, with about 20 more who walk through to get to the kitchen and go to seminars) is casual: jeans and t-shirts are normal. There are a few people who dress up on days that they lecture to undergrads, or just wear collared t-shirts or polo shirts. Informal dress is standard.
Now that the weather is summery, some people have switched from a t-shirt and jeans to a t-shirt and shorts. That's fine. Today is particularly sunny and warm (84F, 29C) and so I am wearing a sun dress. It is modest (school-appropriate) and comfortable, made of cotton and tie-dyed. I think of it as a very casual garment, the sort of thing I'd wear over a bathing suit when going to the beach.
I have received several comments from my fellow grad students (all men) to the effect of "why are you all dressed up?" and "isn't that a bit formal for the office?" No. It's very casual. I wouldn't wear this to a formal event, or even a normal dress-code-abiding office, because I would look frumpy in a wrinkly tie-dye sun dress. I tried to explain this to one of them, but he just didn't get it.
I eagerly await the return of the (only) other female grad student (in this research group).
This post's theme word: peignoir, "negligee."