Yesterday I tipped a lot of money and now I'm thinking a lot about it.
why are you thinking so much about yesterday's tip ?
Because the service was so bad that I felt like I should not leave any tip.
It's ok if you didn't like the service at all and you decided not to spend your more money by giving any tip. you don't need to think so much over it.
It's not that difficult, the service was bad, I didn't have to give the tip.
Who said that it was? You just shouldn't be thinking so much about it, and I agree that it is okay to not tip if the service is bad enough-- just remember for next time you have poor service.