During the summer I usually wear just a standard black t-shirt and jeans to work (office job but my role is not typically customer facing, I keep a shirt and tie in my office incase I need to do a quick video call) because it's just too damn hot and i'm comfortable in it. I had a very fashion conscious account manager nagging me about it for a while, all light-hearted and she can take her fair share of ribbing right back. One day I flat out told her "the day I start caring about how YOU think I look is gonna be a cold day in hell" Never heard another nagging comment since.

Sometimes it's best to be blunt. Confidence is everything. This is how I am and if you don't like it, you can go screw.