I'm thinking of spitting in the dentist's face after a painful and expensive procedure.
That seems crude. Did something go wrong?
No, I don't like the way he speaks; that is why I want to do that to him.
I don't think there could be any good reason to spit on someone but that definitely is not one. It's wrong to spit on people and I would advise you not to do it. He could probably press charges for assault or something.
I just want to do it, I hate him. I'm going to proceed the plan.
It can be dangerous to mess with someone who has drills and drugs working in your mouth. You can find a different dentist if you hate him so much.