I'm going to only tip $20 for a 5 hour haircut
Why do you want to tip that amount?
Yes, I don't see why I should tip a lot.
Consider the service you are receiving and the time and effort that is being put in to complete your service. It would be rude to give a small tip for good service.
That's not my problem. I don't like the service and I'm going to hurt the place by not tipping very much.
I think if you don't like the service, you should change hairdressers and not return next time. Tipping is customary, but it is not required if the hair dresser did a poor job on your hair.