1. any size Medium shirt (especially a T Shirt) worn by a man whose body-size would usually require a size Large shirt for comfort, worn for the accentuating affect it gives to musculature of the torso and arms; The resulting effect is similar to that of a medium-sized person wearing a size Small shirt.
2. a nickname for a man wearing such a shirt
Rob - "What size shirt you got on?"
Jeremy - "Fuck you."
Rob - "The price you pay when you rock a shmedium in this place."
-Season 3 Episode 8 of 'Rob Dyrdek's Fantasy Factory'