Tipping is supposed to encourage prompt and attentive service in the hospitality industry. The standard contemporary protocol for doing so relies on principal based calculations, viz. a percentage of the cost of an associated purchase. In the restaurant business, this principal is usually the meal total before tax (although the minutia of these calculations, whether before or after tax, is irrelevant as I intend to argue that the fundamental premise is flawed). The standard tip for the waitstaff at a restaurant in America is 15-20% the principal. This is widely accepted as the standard calculation. It is wrong.
If what we as consumers are tipping for is attentiveness, expediency, amicability, and expertise in the staff, then basing our calculations on meal prices is only slightly less arbitrary than basing them on the number of letters in the restaurant's name. Consumers should ask themselves how meal prices are in anyway related to the competency of the waitstaff. Unless those meal prices are inflated as a result of adequate base compensation for the staff, which they most often are not, there is no connection that would lead a reasonable tipper, devising a tipping strategy from the ground up, to associate the quality of service with the price of the meal.
To be fair, I will describe how I see our current system of tipping to relate to waitstaff service. Expensive restaurants draw expensive clientelle who leave large tips. Large tips elicit more talented waitstaff to apply for those restaurants. Expensive restaurants employ a higher quality service staff. This higher standard of service is in part what draws expensive clientelle to expensive restaurants.
This causes problems.
Why does the service provided at a restaurant rely on the price of the food? Under this system, an assumption is made that meal prices, chiefly reflections of food quality, are inherently tied to service quality. Consequently, individuals who cannot afford to dine at Michelin 3-star restaurants or eateries found under the "$$$$" filter of Yelp should not expect quality service. But there is no real reason why a very talented waiter at a small, cheap sit-down restaurant should not be afforded the opportunity to make a decent wage notwithstanding low meal prices and provided they fulfill their own duties with skill and competency. What does the quality of the food have to do with the quality of the waitstaff?
Furthermore, tipping as a percentage of meal prices creates a principal-agent dilemma wherein the waiter has incentive not to act in your best interest. Their own interest is in selling you the most expensive items on the menu, regardless of the freshness of the ingredients or the chef's competency in its preparation. They will snub the humble diamond-in-the-rough dish that the chef is incredibly adept at preparing for the haughty, and incidentally expensive, nouvelle cuisine which the chef is sourcing from the same recipe sites you browse at home. Is this what you want to tip your waiters for? Shouldn't we tip based on the actual services which the waitstaff is providing to us?
Here is my suggestion: per-item tipping. This process is most common at the bar where expediency of payment is desirable, especially on those crowded nights when orders are placed, received, and paid for all while grinding crouch-to-ass-to-crouch with the five other patrons squeezing into every five feet of bar top real estate. You generally tip the bartender a dollar for every drink they deliver. If you order two drinks, you tip two dollars. This system is convenient for the bar, but it's downright sensible for table dining. Bartenders have to create the drinks you're demanding, often times requiring more skill and effort to create the fussier concoctions that might carry larger price tags. It would actually make more sense to tip them as a percentage of the cost of the drinks. However, waiters and busboys do not create the meals you enjoy. They simply act as ferries and culinary tour guides, and it would be nonsense to judge a tour guide on the merits of anything but their presentation. Only a total ass would elect to tour the Sistine Chapel, then finding that they have no taste for the art, direct their frustrations at the tour guide.
When you go out to a restaurant, consider how many items you're ordering. Consider how often you're requiring the waitstaff to ferry to and from the kitchen to your table. Consider how many plates you're asking to be carried to you. These are the bare minimum duties of waiters and busboys. Then, when you have accounted for their bare minimum duties, decide an adequate percentage of that base per-item tip to add on top as a show of gratitude for prompt, friendly, and helpful service. For example, if you're on a date and you order two drinks, two appetizers, two entrees, and split one dessert, that's a per-item total of seven dollars. That is your base tip. If the service was slow and unenthusiastic, you can leave it at that. However, if you found the service particularly pleasant, consider adding 25% of that base tip to the total, or whatever percentage you feel adequately expresses your satisfaction.
With the per-item tipping system, you can reward waitstaff at any establishment for their competent service regardless of what you decide to order. You are compensating them for the work they are actually providing for you and not lumping their services thoughtlessly into the overall prices in the menu. You can sit-down at a cheap, dive-y pub and still tip the cute waiter or waitress, who briefly painted over your loneliness with impressively feigned flirtation, an adequate sum. It is a purer, more direct, and fairer expression of gratitude. It also requires far less mathematical gymnastics.
So consider revisiting your typical process of tipping the next time you dine out, and ask yourself what it is you're really adding that tip for, because like every gullible sorority sister will confess, the tip is never just the tip.