I want to live in a world where we’re all judged by the quality of our hearts and our minds first and foremost. That’s the world I want to exist in, but it’s not the world that I exist in, none of us do.
Like it or not, the disappointing reality is that your manager will judge you by your clothing. If you dress in dirty clothing, you will give off the impression that you’re the sort of guy who dresses in dirty clothing (which you will by definition be!) Now, substitute any other adjective into that previous sentence and it will still be true. If you dress overly formally, your boss will get the impression you’re overly formal. If you dress overly informal, your boss will get the impression you’re overly informal. If you dress in heavy metal t-shirts every day, your boss will get the impression you’re the guy who dresses in heavy metal t-shirts every day. I’m not arguing that any of these clothing preferences are good or bad, I’m just arguing that every article of clothing you wear has strong cultural connotations, and you will be associated with the connotations of your clothing.
And not just your clothing, but every aspect of your physical appearance, unfortunately. You want to dye your hair red, white, and blue? You will be seen as signaling that you’re part of the team of people who dye their hair red, white, and blue.
The same applies to every other aspect of your appearance. These include nail biting, or, sadly, by how much your weight deviates (either up or down) from the expectation of the context. And the “up” or “down” conveys different messages, again that are context and culturally dependent. Take the nail-biting example: they notice these details, and it definitely implies anxiety. So, do you want to give off the impression that you’re an anxious person or not? Perhaps you want to approach your boss as calm, cool, and focused (in which case it makes sense to not bite your nails.) Or perhaps you want your boss to know that you’re so emotionally engaged with and attached to a high-risk project your team is embarking on that you’re nervous, and thus your nail-biting and short cuticles help convey that message. You need to choose the strategy that’s right for you, I can’t help you with that. I can just observe that they will notice these details, so you need to get the details right.
The broader version of this is that everything is a signal and that your manager’s job, to a large degree, is smelling bullshit. If you try to convey one message but the details like your physical appearance aren’t consistent with it, then yellow flags will go off in his mind. Or worse, perhaps red flags.