A sweater vest and grey sweatpants make for the ultimate relaxed style for any guy. Complete this look with a pair of grey athletic shoes to infuse a sense of stylish casualness into your look. As the weather is getting warmer, it's time to get rid of those heavy winter gear and choose an ensemble that's lighter, like this one here. This combination illustrates how to score in the casual fashion department as a 20-year-old man.