1. Are you in America? You should tip. At least 15 percent, 20 percent if you're civilized and financially comfortable enough. Can't do math? There's an app for that.
2. Did your server a.) spit in your food in front of you? b.) use a racist term in addressing you? c.) lean over and grab your breast? d.) something equally heinous? e.) all the above? No? Then you should tip. If any of the above did happen, not only should you not tip, you should immediately stand up and demand to see the manager. You should also utilize social media to bring the motherfucker down.
3. Are you considering stiffing due to the quality of the food or the amount of time it took to arrive? That's likely not the server's fault. If the food isn't to your satisfaction, don't go back. If you walk into a crowded restaurant or bar, understand you have agreed to wait — if you don't want to wait, Humboldt has no lack of other restaurants and bars that would love your business. If the service is definitively and truly mediocre, you may reduce the tip to 10 percent — but you should still tip. (Your bad mood is not an excuse. The waiter is not your jerk boyfriend or smarmy boss.)
As a former cocktail waitress, food server, bartender and barista, I would also like to offer this bit of advice to everyone in those fields who doesn't already know it: No matter how busy you are, try to make eye contact, preferably with a smile, with the individuals waiting. Often, when overwhelmed, bartenders in particular will ignore new customers until they can fully turn their attention to them. But a little acknowledgment goes a long way — if people feel noticed, they're much happier to wait around. They can see you're busy, after all. But if your potential customers feel invisible, that means they also feel slighted, and will likely leave and not return.
4. Are you planning to stiff your server as a statement against the practice of tipping, which, one could argue, is an unfair and inconsistent way to reward people for doing their job? You should still tip. Sure, it doesn't make much sense, a system in which opening a bottle of beer equals the same dollar on the bar as making a perfect Manhattan. Nor does a waiter serving overpriced fine dining meals necessarily work harder than a waitress slinging hash, but the former makes more money due to the percentage system. Understood. But, for anything less than gross misconduct, failure to tip is akin to stealing money from your server's paycheck — the federal government allows servers to be paid less than minimum wage on the assumption that they make up the difference in tips. Until our whole system changes, make your stand elsewhere — and tip.
5. Are you ever going back to that restaurant, coffee house or bar? Because once you establish yourself as a cheapskate, the service isn't going to improve. You may think you're teaching someone a lesson, but what you're doing is encouraging staff to care less about you at best and sabotage your experience at worst. Even when the experience is truly bad, angering the people who are making and serving your food is never a good idea, at least if you want to eat it. Just be a decent human and tip.
BONUS: What if you failed to bring enough to tip? Oh, this is awkward and best avoided. But if you find yourself stuck in this situation, prevent adding insult to injury by being honest. Tell the server you underestimated the bill and don't have enough to tip properly. Promise to return and take better care of him or her next time. Then do so. If this happens when you're traveling or otherwise unable to return, tip big the next time, wherever you are, in hopes that karma is real and your attempt to balance wrongs and rights pays off.