Too many guys wear shirts that are too big for them. I know fashion is subjective. I know what looks goofy to me might look fine to someone else. But. The shirt is too big. You want to know how to tell? Look at the shoulder seam. If it's on your arm, the shirt is too big. With your arms at your sides, the seam should be about where your shoulders drop off (approximately, since we all buy off the rack, right?).
This isn't an arbitrary rule of thumb. This is engineering. Point one. Your arm moves. The shirt will flex and move at the shoulder. Seams are stronger than fabric. You want the seam at the point of stress. Point two. Your shirt will break at your shoulder. It will also break at the seam. If the seam is in the right place, there will only be one break. If it's in the wrong place, your shirt will break twice. That does not look good. Point three. Clothing manufacturers know this. They size the rest of the shirt appropriately. Big clothes on small people makes them look smaller. Big clothing on big people makes them look bigger. Wear the right size. You'll look better.