"Oh, man, I don't know why I'm so horny," the jock said rubbing the pouch of his jockstrap. He headed to the sauna wearing only his jockstrap. He grabbed a towel, and sighed as he laid down on the wooden bench in the otherwise empty sauna, "Now for some relief!"
He immediately began jacking off off into his jockstrap. Jeff was stretched and horrified. His screams became more incessant and louder - at least to Jeff. The jock seemed oblivious to them.
"AAaaaaaaaaaaaaah!" he moaned as a massive wetness exploded into the pouch. Jeff felt the liquid drenching him, oozing through him and saturating him. The massive load of cum quickly became tacky and hard in the hot dry air of the sauna. Jeff was silent trembling at least he would have been if he weren't a jockstrap.
The jock strolled back to his locker, and peeled Jeff off his body. He lay him on the bench, and straightened him out, just the way the jockstrap had been when Jeff found it. Then he headed to the showers.
He sauntered by Jeff, and dressed. He was holding his open gym bag, and looked down at Jeff.
"You mind handing me my jockstrap?"
"Huh?" Jeff said opening his eyes. He was lying on the bench, he was human again. He sat up, and found the jockstrap under him, and handed it to the jock, "Uh, here you go, sorry, I uh-"
"You were playing with my jock four or five hours ago, and got merged with it, right? My load of cum changed you back-for now. So be here tomorrow at the same, and I'll put you through another workout," the jock ordered. He turned and started to leave.
Jeff opened his mouth. What if he didn't show up? He spoke up, "Okay, see you here tomorrow. Uh, what's your name? Mine's Jeff."
The jock turned and shook his head. "No, your name is Jock Strap. My name is Mitch."
Then he was gone.