I recently was reading a novel, and there was a passage'"he was dressed like any other retiree, t-shirt, shorts and flip flops".
I cracked up because that is how I dress
Yup, that's the official uniform of retirees. As for you not yet retired, remember you want to "dress for the job you want, not the job you have."
I used to walk around the office in stocking feet. Told everyone they should see me when I come in on my day off; bathrobe and slippers! Never actually got that far, but I did have them wondering.
I've been doing a lot of yardwork lately, and I'm running out of t-shirts that don't have holes in them from clearing pricker bushes. But there are also fewer and fewer times I really need one without holes