When you open the box, you see a baseball jersey, cap, pants and black cleats. "Secret admirer? This person doesn't know me at all. I hate sports, and I'm terrible at them."
You put the box down and begin to walk away, but part of you is drawn back to it. You consider the contents again and reach for the cap. You put it on your head and it fits perfectly. Something was happening to you, but you had no idea what--and no control over it.
You take the cap off again, then strip down to your skivvies and dress yourself in the uniform. It fits like a glove. You walk over to a nearby mirror, and watch helplessly as you begin to change.
On your face, dark brown stubble grows out, like you haven't shaved in about three days. Inside it, a bulbous growth begins to protrude from your left cheek--chaw tobacco.
Though the uniform fit well enough before, your muscles expand, your arms becoming powerful weapons, rope-like sinew blowing up all over your forearms. Your legs become thick tree trunks, and though you can't see it, your pecs inflate to about four times their previous size as canals form between eight brick-like abs.
When it's all over, you turn to your right and spit a jet of brown saliva all over the floor.
Unable to stop yourself, you adjust your massive package as you jog out the door on your way to the park.