When I play live (local leagues or at a casino) I will wear either a CardsChat t-shirt or hoodie. I also use a CardsChat card protector. Usually someone there will ask me about the forum.
In general, I go for total comfort. Live you're going to be playing a long time (hopefully) and it can get cold in the room.
It's very interesting question, because different people has different style and you have 50/50 percent chance to meet a professional pokerist, but from the first hands you will definitely know who is this one. What about me, I preffer as much as comfortable clothers because it helps me to concentrate on game!
At home I always wear shorts or shorts, it's very hot here on the island, when I go to a poker house, jeans and a polo shirt, even though I've already been wearing a sweater
Look friend, I'm still trying to get chips, to get my C.C. Pullover Hoodies so I can really be prepared to destroy the poker tables in my city.
But until then, I don't feel prepared.
I just wear my usual clothes, never dressed up for the occasion. Bu now as you ask, i think for live events clothes could be important, i'll be thinking on this