Jake quickly pulled off all of his clothes. He picked up the pair of old briefs. "Old briefs" was a bit of a misnomer, as he had never actually worn there. They had been gifted by a relative a few years ago, back when his cock was just beginning to grow. He had complained of a lack of support, and the briefs were designed to support someone of average size. They had a pouch in front to rest the balls, and Jake wasn't sure how to use them otherwise. He had always used boxers, and so he was a little miffed when his relative couldn't even check the correct type of underwear. Nevertheless, it was now serving its purpose in attempting to support Jake's soon-to-be monster cock.
Jake pulled them on and made sure to lift (or attempt to anyway) his meager balls into the pouch. Absolutely no bulge showed on the front of his briefs. Jake was disgusted. Opening the app, he first tried his new "normal" size of 5 inches soft and 6 inches erect. Jake watched as what appeared to be a baby carrot slowly inflated to a more normal size, one that he would expect on any average boy at his school. There was a small bulge but nothing really extraordinary. Jake couldn't wait to really turn up the heat. But he decided to go slowly.
Opening the app again, Jake adjusted the sliders into the area he defined as "big". That meant adding 2 inches to every measurement and upping his ball size. Jake keyed in the appropriate measures for 6 inches soft and 7 inches hard. He also adjusted the ball slider to 4 (egg sized) and hit Enter.
Gleefully, Jake watched as the small outline of his cock inside his briefs got bigger. His balls began to swell up, bigger and bigger until they filled the pouch completely. The briefs began to bulge out as his cock lengthened and thickened up. It was now a respectable size, and just slightly too big for his briefs. They bulged out with the outline of a bigger-than-average cock underneath the fabric as they struggled to contain Jake's now sizable endowment.
Almost teasingly at this point, Jake added just one inch to his cock's measurements and hit Enter. The already fairly-big bulge grew even more, as Jake's cock, now thoroughly out of room in his briefs, pushed outwards. Jake was practically salivating at the seemingly monstrous bulge he now had, but he had more in store. Opening the app for the last time, Jake upped the sliders to the same settings he had before: A full fat 12 inches soft and 14 inches erect. But he paused... could he even go higher? He could always undo it later, right? Jake slid both sliders upwards more... settling for 15 inches soft and 18 inches erect. He keyed in a new size for his balls as well, upping them to 7 (softball-sized). Then he settled in to watch the show.
First, his balls began to swell, pressing the fabric of the briefs out further. Already completely filling the pouch, they began to stretch the pouch out, creating two more bulges on the exterior of the briefs that grew larger and larger. As Jake's balls passed the size of tennis balls, they actually became so large that Jake had to spread his legs wider to accommodate the increasing amount of bulk between his legs. His balls passed the size of large apples, and finally settled on the size of large softballs. It looked ridiculous, and the balls were so oversized for the pouch that one of them was beginning to fall out and would have if the space hadn't been occupied by Jake's soft cock.
Then, Jake's already big cock began to get fatter and longer. Now pushing 10 inches, it began to deform and stretch the fabric of his briefs further. Jake could clearly see his large cockhead through the briefs, because his cock was being pressed against the fabric by the pressure building inside the briefs. He moaned loudly, as the enormous pressure translated into pleasure.
Jake's cock was now a full 12 inches long, and it was still growing. The briefs were now stretched to their absolute limit, and they could take no more. The seams of his briefs at the elastic band began to break one by one as the material separated. Jake heard each string, POP POP POP. The pressure kept increasing. And finally, it could take no more. With one final enormous RIIIIIIP, Jake's briefs completely fell off his body, exposing his crotch.
And what a crotch it was. Jake could hardly believe his size as he looked down. His long 15 inch cock was the thickness of a Coke bottle, resting on two enormous nuts. He didn't think he could ever fit it into any of his clothes. He could try others though, right?