The answer depends on what they feel most comfortable in. If fat guys are more comfortable wearing tight clothes, they should wear tighter clothes in the summer to stay cool. They should dress accordingly if they're more comfortable in baggy clothing like shorts and T-shirts. It is okay to dress however you want, no matter your size or shape. It's disrespectful when people make fun of someone for how they dress because everyone is different, and everyone should be accepted for who they are.