How well do you tip?

Standing at the checkout counter of Sports Clips:
He got a haircut. We have a coupon.
She asks the stylist, a cute Asian girl, to break a $10. Gets two $5 back.
He takes out a $10. He and she look at each other confused.
He gives the stylist $15 and the coupon. The stylist gives her the receipt. Thanks, happy chit chat, we leave. He and she walk out, get in the car, she is thinking.
She "do you always tip that well?"
He "well I try to, why?"
She looks at the receipt "that was a very generous tip!"
He "what do you mean? the stylist did a good job and she knew her football!"
She "well that was a $17 haircut with a coupon that says new clients get a FREE haircut and return clients get a haircut for $10."
He "so $10 haircut and $5 tip, right?"
She "you told her you have never been to that location," looking at the receipt that had a seventeen dollar haircut and seventeen dollar credit.
He, getting excited, "are you telling me that I just gave a $15 tip? I just paid a hundred and fifty percent tip??"
She "um..."
He, calmly but worried, "well can we go back and get my $10?"
She, laughing hysterically, "no. Kim, your stylist, will remember you forever, you will always get great haircuts."
He, disappointed, "it was a good haircut, but not 150% tip good!"
She, giggling, "well just pretend you paid $10 for the haircut and gave a 50% tip. No worries"