How about becoming...a deer? Deer were cool, right? He'd seen plenty wandering around the backyard of his neighbors, all proud and upright, doing whatever they felt like doing. Very well then; he hit the button on his computer marked "Deer: male".
He took his clothes off, and the moment his socks were off, the changes started. Oddly enough, they began with his muscles contracting and expanding until he was ripped like those big jocks on his high-school football team. Cool.
Then the other changes began. Thick brown fur sprouted on his chest and quickly covered his body, including a small tail that grew out of the tailbone above his ass. His thighs became sleeker and more compact as his feet shriveled into small hooves, and he quickly found that he could now either stand upright or on four legs. His hands were bigger now as well, with the middle fingers gone, leaving him with only eight digits.
Yet for all this, he still had his human head. That changed rapidly. First, his neck got longer. Then his face stretched out into a muzzle, with a small black nose on the end and his eyes on either side, giving him much greater awareness of his surroundings. His ears were now protruding from either side, and they could hear very small, very sensitive sounds. And for the finishing touches, a pair of magnificent antlers appeared on the top of his head.
He was a deer-man now. And suddenly, he found himself outside, eating some green plants. It was then that he noticed someone: the most beautiful deer-woman he'd ever seen. The sperm in his penis started to drip out as he became fully erect. It was time to make some babies.