Tech companies, and startups in particular, are known for relaxed dress codes. I don't believe people's attire has much effect on their work performance, but I sometimes wonder how software engineers (as a profession or individuals) would be treated differently if they wore nicer work clothes (e.g. no hoodies or logo t-shirts).
Do you dress up for work? Does your office have an unspoken dress code, pressuring people to dress up or down?
On the other hand - I do like to wear "better" clothes. They definitely do work in places like banks, offices, etc. where you want to get something done efficiently. They will even get you a drink at the bar before a student in a hoodie sometimes. There's a stereotype of a professional and expensive look - play it right and you can get a slightly better treatment.
Additionally if you do feel that you make a better impression than people around you, your charisma will improve making the "better clothes" a kind of self fulfilling prophecy. This could work just as well for having the most geeky tshirt in an appropriate group.