You'll give him a ruined orgasm

"All right" you relent "but your hands will be tied up. And I will only give you a handjob."

"Yeah, yeah" he agrees without thinking" men are so stupid when horny.

You find some string it's not very strong, but you don't need to keep him immobilized for long. You tie up his hands and smile at him:

"Oh, such a nice cock. Let's stroke it."

You use both of your hands, you slowly work his cock, but he was indeed very horny and pre-cum begins to leak from his cock. You know that you need to time this moment perfectly. You start stroke him quickly with crazy speed.

"Oh, go, oh god" from the tone of his voice you know that the moment is now. So you stop stimulating him, you take your hands off. He whines, he buckles, but he can't free his hands. Then he cums. But it is not a typical orgasm, he doesn't cum with a fountain. It barely flows out of his cock. He let's out a loud whine, you hope your parents didn't hear him.

"Emi...why?" he looks at you. He doesn't seem angry, he's similar to kicked puppy.

"You need to learn" you say gently "that instant gratification is not worth it. It's better to wait a while and then you'll get full reward. Do you understand?"

He nods his head although he looks like he is on the verge of breaking down into tears.