There are certain indicators that let the wearer know when the gents underwear is not the right size. If the elastic band is loose or moves when you bend or squat, it indicates that the underwear is big for you. If the under wear sticks to your skin uncomfortably, rides up to your thighs, and restricts your movement, the size is small for you.
Nothing is worse than wearing underpants for men that makes you feel cramped and uncomfortable, so opt for the right fit and right size.