My encounters with an autistic child. I'm going straight to hell with a big NOOOOOOPE face. Thoughts?

Let me set the scene for you: I am a music instructor. I teach children to play and read music. They're all wonderful kids who are attentive,they listen the first time I say something, I never have to repeat myself, silence them, etc you get the idea. Now, one of them has a younger sibling. Let's call him Derple for more than one reason. Poor Derple has autism and at this young age, not only is he a typical child, he has a bonus package of autism on top of his typical child-like behavior. "Brilliant" I thought. He's a wonderful kid, cute in his own way, BUT he has to tag along every lesson without exception and I not only can be a little hyper myself, I also am not exactly known for patience and tolerance. Every other minute I hear "Misterrr Deeeeeerrrrrrrrrrp" (yes he actually pronounces my name with extra long syllables) and it gets on my nerves. Alot.......A-fuckin-lot. And I feel horrible at the end of the day for it though I manage not to say anything about it. The thin line between being a complete asshole is voicing those wonderful thoughts you have to the public. I might think it, but damnit I'm a nice guy and I want to stay that way. But the "Mister Deeeeeeeeeeeeeeeerrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrp" is really starting to get me peeved. Does anyone have a solution or any thoughts?