HOW DO I EVER GET OUT OF THIS?

So my little brother is four years old and STILL wears diapers. A lot of times I do tease him about it, especially when he annoys me. He always cries dramatically when I strike back at him. Then the other night, I teased him again and my parents flew off the handle. Said a bunch of angry words and all but they also told me that starting on summer vacation, I'm going to start spending time in diapers myself. I tried saying sorry every day but neither parents will listen.They keep replying we'll see how sorry you are when you're in diapers. Is there any other way to persuade them to change their minds? I mean, he doesn't WANT to use the bathroom! I'm 16.