I would never show up to a business meeting, especially with people I did not know well, in a tank top, shorts and tennis shoes. Even if I was offering to invest money I would want to create a respectable image.
Nice (clean) casual clothes might be acceptable.
Grow up and play the game with the big dogs
Then again, if a Warren Buffet type wanted to show up in his underwear: I would probably meet with him and take his money but I really doubt he would ever consider showing up appearing like that at a business meeting. Some people have class.