Her panties

Digging around in the laundry bin, he quickly finds something of interest. He pulls the small, thin material up to get a better look at it. The soft light from the bathroom window easily passes through the sheer material of the tiny thong in his hand.

Swiftly dropping his trousers and boxers he kicks them into the corner of the room and pulls the panties up, over his thighs. The waist band, if you can even call the small piece of string that, is much too large for his manly hips so he has to hold it in place. He jumps slightly at the alien sensention, similar to a wedgie, of a second piece of string becoming firmly wedged between his buttocks. His balls spill out either side of the small, triangular material at the front and the tip of his painfully hard erection sticks out over the top. He glances in the bathroom mirror, his face flushing red as he stares at the man in panties staring back at him.

"This was a stupid idea" he thought to himself. Just as he was about to remove the thong and attempt to sneak out of his mother's room he noticed something strange. His balls seemed much smaller than usual, he could have sworn they were hanging fully out of the thong but now they seemed to be half under the material. His dick was still hard but it also seemed smaller now, stretching the material into a small tent rather than proudly peaking over the top. He continued to watch in the mirror as his balls carried on their journey upwards, getting smaller as they did so. The material of the front of the panties now sitting almost tight against his crotch as his dick now resembled a button mushroom, clearly visible through the material.

A few moments later, with an almost audible pop, his ball sack ascended into his body and he was left with a tight vagina and neatly trimmed pubes glistening with arousal through the sheer fabric.

"Holy shit it worked" he thought. He creeped over to the door and pushed it gently open. It was a warm day so his mother hadnt gotten under the covers giving Josh a clear view of her sleeping form. Between her legs he could just make out the outline of a familiar shaped dick in the dim light.