Interesting recent article by Michelle Singletary saying you should always tip 20%...
https://www.washingtonpost.com/business/economy/poor-service-you-still-have-to-tip-20-percent-no-matter-what/2019/10/08/e163d2f0-e9d1-11e9-9c6d-436a0df4f31d_story.html

I don't really agree. If it's totally unrelated to service and expected, then just raise the price of the food and the wages of the workers. Why bother pretending there's more to it than that?

Never tip less then 20%

Wait...what? Why would I tip 20% for lousy service? The whole point of tipping it to reward waiters who provide outstanding service. For average/expected service, I would normally tip 15% of the post-tax total, rounded up to the nearest dollar. Outstanding service gets 20%, also rounded up to the nearest dollar. I can count on one hand the number ot times that I have tipped less than 15%, but bad service gets 10-15%. Anything worse than that, and I will talk to the manager (which I have done exactly once).

I have heard arguments that tips should be pre-tax, but, as mentioned above, it barely makes a difference in the amount.

I tend to be generous, but I don't think that the best employees (waiters, in this case) should be paid the same as the worst ones.

Now back to your regularly scheduled discussion about tipping apps.