My rule for customer facing interaction: when talking to a customer or client, always be one notch more 'formal' than they are. If they are in t-shirts and jean

My rule for customer facing interaction: when talking to a customer or client, always be one notch more 'formal' than they are. If they are in t-shirts and jeans, then a collared shirt with no tie is ideal. If they are in collared shirts, then put on a tie and jacket. If they are wearing suits, so should you. Investors are a totally different beast. In my opinion, most of them aren't going to be too concerned about how you dress other than judging if you present yourself well to your customers/clients (see above).