I usually wear a large size, but on this shirt I bought a medium size because I need a tight (athletic) fit, but the shirt, even a size smaller, is too big!
Pros
100% Mens Sports Fashion Cotton T-Shirt - Basic O-Neck Long Sleeve T-Shirt Sport Solid Color T-Shirt - 5 Colors
Cons
Medium fits like a large. I have a muscular torso and it's still VERY loose.