Dress for the function. This ain't rocket science.
You want your shoes to stick to the floor. I.e., good all around sneakers, or wrestling shoes.
You want to be able to see yourself in the mirror, to make the mind body connection and to prevent any delusions: shorts that show your legs, and a tank top.
You want decorum and comfort. I.e. something like UnderArmour that prevent chafing, and doesn't expose your private parts, as well as provides some support.
Don't wear sweatshirts, hoods, or sweats. They only serve to make your body temperature rise, and cause a substantial deccrease in exercise performance.
In other words, don't be a moron. Sandals aren't meant for the gym. You're an idiot if you overheat your body. Pick up your weights; don't walk in front of a seasoned lifter. Just plain courtesy. It ain't hard folks.