I've decided I'm not going to tip my barber.
Did he give you a mohawk when you requested a Beatles cut?
I usually tip him, but not when makes my hair look like shit.
It is upsetting when somebody doesn't do a good job, but you have to consider whether it is really that bad. He might not want to do your hair again if you don't tip him.
It's not like his job is hard, it's just a haircut.
You have to communicate with your barber. If you don't like a cut, tell him what you prefer and so he'll know for next time. If you stiff him, all you're doing is telling him you didn't like what he did -- without giving him a chance to rectify it next time.