If you got it...share it with those who provide you with a service.

If you ain't got it, still tip 18%.

Not tipping is permissible if you've be royally wronged, but it should also come with some sort of verbal complaint.

My wife worked over 15 years in the restaurant industry (I only logged 8 years). She sometimes tips over 50%. I sometimes remind her that we are not rich enough to do that.

NOT CRAP.

Don't remember if I posted on this or not, but anyway: tipping is required, and tipping well is required unless they did a truly shitty job, in which case you're perfectly privileged to leave a shitty tip. It would take a lot for me to deliberately stiff someone.