f I receive poor service from a waiter/waitress in a restaurant, what's the best way to show my displeasure?
OK, I'm coming back into this.
I grew up in the restaurant business. Back in the 60s, the custom was to tip 10%; more for really good service, less for bad service. Somewhere in the 80s, that number became 15%. Today, it's 20%.
That makes no sense at all. Food prices have risen in direct proportion to the cost of living, so a 10% tip today has the same impact on a servers' earnings as it did in 1966. A bit more, actually, as sales taxes are double what they were then, and virtually everyone tips on the total, including tax.
I'm a poker dealer. I work in a tipped position, so I tend to be a big tipper. That said, it is critical for people to tip according to the service they get. In a capitalistic economy, one of the most important concepts is Economic Darwinism: Businesses that provide a better product do better, businesses that provide a poorer product fail. In this respect, your server is a business.
If people tip according to the service they receive, good servers will do well, and bad servers will not, and will eventually go find something else to do. Their slot will be filled by another server. If they're good, they thrive. if they're not, they go away. Soon, the overall level of service improves, and capitalism works as it should.