Whitmore is just wrong. Not tipping a taxi driver is fine; but tipping them small-change is likely to elicit a stream of curses - because it's insulting.
It probably depends on how small the tip is, but you're right. Leaving a substantially undersized tip is a statement that you were unhappy about something. Leaving no tip isn't.
I may or may not have allegedly left a single penny as a tip at restaurants before for exceptionally bad service. Shoved down the credit card holder pocket thing so they had to fish it out.
