People who dance to the beat of their own drum rather than conforming automatically, garner a lot more respect from me. Otoh, people who are rebel against the "norm" just to be edgy are very obvious and are a detriment to their credibility on the onset.

I couldn't care less if someone's wearing shorts, sandals, and a t-shirt to give a presentation if they obviously know what they're talking about.

Wear what's comfortable, with some respect to common decency - wearing a speedo to give a presentation on a JS library probably won't warrant a great response (though I'm sure stranger things have happened).