One is the idea of a percentage: how does that make any sense? When I go out for a rare nice dinner and the tip alone ends up being $20 or so, I ask myself: did this person/restaurant really do any more than the server of the last entire meal that cost $20? Of course not, and yet somehow it would look weird to pay $40 for a $20 meal with tip, for the same service?
Another inconsistency is where to tip. Yes, tip at restaurants but what about the zillion other places that sometimes explicitly and often implicitly expect tips? Do we have to slip a dollar to just about everyone in case they expect a tip?
And finally, the inconsistency in who tips. Sometimes I tip generously because I assume there will be other people who just don’t tip at all, or tip poorly, and I feel some obligation to balance the pot. I don’t know why, it just seems like the right thing.
It would make a lot more sense to end all these charades and just show exact prices. (While we’re at it, let’s make sure utility companies do the same, up front, no fees.)