I felt a little bad the other day because I got upset with my son. He always panics when I have to buzz his hair and I was so frustrated. 
Dealing with kids can be like that. Is there something about doing his hair that he is scared of?
I think it is just the noise of the buzzer that makes him nervous, but he literally just screams and cries. It definitely doesn't hurt him at all.
Sounds like a bribe is in order. Then it's a win for everyone.