Gene locked the door to his room, and stood in front of his over-sized, full-length mirror. He was skinny, awkward, clumsy, and not particularly good-looking. He wasn't ugly or anything - just plain. He had tried some simple exercises - push-ups, sit-ups, and all that - but it hadn't done much good. He was lean, just not buff.
Looking in the mirror, Gene thought back to the comment he'd heard in his head. "Some muscle, huh?" he thought. He became angry, "Why just 'some'? Why not 'quite a bit'? Or 'a lot'?"
His brows furrowed, and he muttered, "Hell, why not just make me into the biggest fucking bodybuilder in the world!"
Gene felt a strange tingle run through his body. He looked in the mirror, and was puzzled. It was as if the image were shifting, as if the mirror had become unstable. But then he realized that only his own reflection was changing - the portion of his room that the mirror reflected wasn't changing at all - except that there seemed to be less of it, as his reflection grew to take up more and more of the mirror.
Gene felt his tee-shirt become tight across his chest. His mind reeled, as he watched his transformation in the mirror. A pair of round mounds seemed to be pushing themselves out under his shirt. At the same time, his arms bulged, twisted, and grew, filling out the sleeves of that same shirt. The sleeves rode higher and higher, as broadening shoulders pushed into them, forcing them to reveal more and more of his increasingly large, increasingly round arm. His forearms thickened, creating an increasingly severe taper down to his wrists. But even his wrists seemed thicker, attached to a pair of ever-larger hands.
Gene's eyes went to the reflected floor, upon which rested a pair of feet that were beginning to experience pain. He watched in fascination as his sneakers stretched, trying to accommodate his growing feet. Then the laces began to snap, and Gene's shoes came apart, as huge feet burst out of them. Those feet were connected to thick calves, which bulged with round, succulent muscle. Above his knees, Gene supported the most immense thighs, which were ripping through his shorts, like huge hard tree trunks, sweeping out magnificently.
Looking up, he saw that his shirt was ripping as well, unable to contain the huge shoulders, broad back, amazing arms, and ridiculous pecs that were stretching it in several directions. With a single, powerful motion, Gene ripped the rest of the shirt from his body, and then repeated the process with his shorts and underwear.
He stood and gazed into the mirror, mesmerized by his own reflection. Or rather, what he could still see of it. The mirror could no longer contain all of him; his shoulders were partially cut off, and his head was not visible at all. Gene didn't care. He lifted his huge arms, and flexed, marveling at the size and shape of his monstrous biceps. Somehow, he knew that he had grown quite a bit - he was now seven feet tall, and weighed in at 450 pounds.
Gene laughed - a low, rumbling sound. He was now, "the biggest fucking bodybuilder in the world" - just as he had said.