Luke reached for the Great Dane costume, then shouted as the curtain was yanked aside. "What the Fuck!?"
A boy no more than 10 or 11 stood in the opening glaring at him. "You took MY costume!" He pointed at the Great Dane outfit. "I told the clerk I wanted that one and he was supposed to hold it for me."
"This is a dressing room, you asshole!" Luke flushed red and grabbed his shirt to hang over his crotch. "I'm naked here."
The kid shrugged. "So what? We're both guys, and nobody else is down here. Can I please have the Great Dane costume?"
Embarrassment gave way to annoyance. "You couldn't fit in that anyway! You need a .puppy outfit, shrimp."
"Do not!" The kid fumed. "The costumes always fit!"
"OK." Luke picked up the Great Dane costume and handed to the kid, who struggled to hold it all. "But I want to see you wearing it. It's gonna look like a hamster in a furry potato sack."
"Fine!" The kid dropped the costume on the floor, and Luke thought he was going to leave it. But then the boy started stripping.
"Dude! Not cool!" Luke tried not to look, but it was hard to ignore the kid 5 feet away from him. In less than a minute the kid was as naked as he was. And obviously just as young as he looked with clothes on. Ignoring Luke, the boy grabbed the costume and stepped into the hindquarters. As expected, it bagged around him and looked ridiculous. Luke smirked. "Told you so."
Instead of getting mad, the boy grinned and hiked the suit up to position the canine genitals over his small nub. Luke started to shake his head, then blinked and stared. The boy had looked younger before. Now he seemed to be more like a 12 or 13 year-old. The suit shifted, and the dog sheath stiffened. The kid reached down and started to masturbate himself through the costume. Damn! He was taller, and more muscular. He had to be 14!
Luke pressed back against the dressing room wall. "You're getting bigger!"
"Yeah!" Even the voice was older, now that of the 15 year-old the boy had become. He arched back and rubbed himself, the sheath pulled down now to reveal a rigid, pink shaft. A dog's dick. He was humping his hand, groaning and didn't see what Luke did - the costume started to roll up the boy's body. The forelegs split and closed around his arms, and paws formed around his hands. He was 16 now, and still maturing. The shadow of a mustache appeared on his upper lip. Then the huge Great-Dane head flopped over the boy's and the costume pulled closed as if invisible hands were working the zipper. The boy gasped and pawed at his rigid shaft, literally now as his hands had become dog paws, and his arms stiffened into forelegs. He swayed, starting to fall, and Luke stepped forward to catch him. Heavy paws landed oh his shoulder and he grabbed the forelegs to steady the boy. The costume head opened its jaws and a large slobbery tongue licked Luke across the mouth. Then the eyes came alive, and Luke was being kissed by an affectionate, mature male Great Dane with a raging boner!