I learned how to tip from my dad. He told me to leave at least 3$ for every 20$ spent.
In defense of your Dad, from what I remember, when he was "coming up" a standard tip for good service was 10% and $3 on $20 was a very good tip.. The next move up was to 15-18%, and then up to 20%.... Honestly, if I didn't have kids that kinda kept me abreast of the tipping scale, I wouldn't have known either.
But, it's still called a tip for a reason, it's extra. Maybe sometimes deserved, maybe sometimes not, or not so much.