You shouldn't, unless you're giving more or less than you think the server has earned by serving you and your table. If you are, then adjust accordingly.

I have always, and will always, tip either 15%, 18%, or (20%+1-cent), if I tip a tipped-wage server. If I'm not tipping them, it's because they did something really BAD, and I tip them nothing and tell the manager why.

To me a tipped-wage server is a waiter or waitress who comes to your table, takes your order, returns to make sure your meal is satisfactory, offers to top off your water-glass if you have one, and generally either clears the table him/herself or instructs the bus-person to do it at the appropriate time. If the bus-person does an amazing job I might give them an additional buck or three, on top of whatever I gave the actual server. The host/ess gets nothing. The barista at Starbucks is not a tipped server. Nor is the cashier at Burger King. Tip jars at check-out are offensive to me. I didn't like it when I worked for a place that had them, and I don't like it when I'm the customer.

Disclosure; I am a happily married man. Any gift for my wife is out of love, not obligation. She is my mate, my best friend and lover. Not a random waitress or waiter.

PS, you deserve the couch. Maybe before your 24th anniversary you will consider suggesting she buy some comfortable new furniture that includes a great couch.

So, I infer from your information that a waitstaff part time job isn't meant to provide a full-time living wage with benefits. So what is with the guilt tripping of customers to tip 10, 20, 25, 30% to supplement the pitiful income of a part-time job to the level of middle class full-time employee.
Maybe the restaurant business needs to rethink how to attract wait personnel without tips. Good pay, benefits, but forget tips. Give waitstaff back their dignity. They would be better off as valued employees than pitiful underpaid quasi-beggers living off the "generosity" of customers.

Working 20-25 hrs a week isn'tsupposed to pay the bills. It sould be to pick up a few extra bucks! Supplemental income! Not a career. Add the $3 to my bill and no one will need to tip.
Think about this. Recently wife and I dined at one of our local CCs.dinner bill @$100. Couple at our table @$100. $40. In tips in 1 hrs. Times 5 ( the number of tables she was handling as far as I could tel). All the other labels probably left as much (or more). On tips alone our waitress brought in over $200 in one hour on tips alone. At that rate she makes more in 10 hrs then I do in a month.

Most fast food employees and many grocery store employees don’t work full time either and most don’t get health insurance so even if they are making minimum wage, they are probably not living in a designer home in the Villages.

Don’t they deserve a tip?

And again, the law requires that waiters get minimum wage. The gap is made up by tips or the employer.

In reality the term TIPS goes back to the 1600's when the word for "to pass" or "to give" was used. The Online Etymology Dictionary states the meaning "give a gratuity" is attested to 1706.

Nothing to do with "to Insure prompt service".

Anyway in some restaurants (in NY) the prices on the menu state the prices shown includes an allowance for a TIP so no TIP is "required". I don't know how that worked out.

Apparently, they have ended that.

https://www.youtube.com/watch?v=sT0JRiFHnDA

Charity is a separate thing entirely. My super wealthy friends have family foundations established for charity. They are not thinking about it every second of their lives.

You could've left her just 15% instead of 20%. Or here's an idea - get a job as a waiter at the CC restaurant, and demand that you get only state minimum wage of $14/hour, and reject all tips. Do that for a full dinner shift three days a week, for 6 months.

If you can handle that with no complaint, your point will be valid.

Get a job? That's you answer. I've had jobs, thank you very much. Never got tips. Now on the doorstep of 80 with impairments I can't do much of anything. But I can see how leaving the small change on the counter has morphed into a pity ploy that is continuously growing like the blob. Once a few coins became a buck. Then, somewhere, somehow it became a small percentage. 5% was generous, but 10% was "easier to figure". (I wonder who suggested that). It had already become "all about the service"? The service? Really? A cup of coffee, tell the cook what to prepare, bring it to me after it's been sitting under the warming lamp for a while, maybe refill my cup once, give me the bill. It ain't rocket science. And now the pre-suggested /calculated for your convenience, amounts for basic servic has, in some establishments are 20%, 25%, 30%. In what universe is it twice as difficult to move a late of filet mignon from the kitchen shelf to my table than a hamburger steak. Why should my food preference cost twice as much fo the same service effort. Scam! Rip off! Everybody knows it, but argues against the reality because we don't want to acknowledge that we are the suckers the restaurants know we are.

We don't eat out that often (once every 2-3 weeks) so tipping is a non-issue. In any case we're not that motivated by price and certainly don't sit there at the end of a meal, calculator in hand, trying to figure out how much an "optional" addition to the cost of the meal should be. If the service is exemplary, I reward it accordingly. But I don't expect to pay for minimal competence.

If the service is lousy, the tip should be zero. Unfortunately, many people don't agree.

My whole point is really about wait service "requirements". In any given restaurant what would basic "C" grade service (what you are already paying the restaurant to provide so that you can enjoy the meal they provide?
What extra can the server do, over and above, to elevate your dining experience to a "B" grade, deserving of a commendation/tip?
What could you imagine a server , given there position in restaurant hierarchy, possibly do to warrant the waitstaff equivalent of a medal of excellence for "exemplary" service over and above the call of duty?
Spilled soup in your lap = D. Apologized = D+
What deserves an "F" ? We won't go there, but I won't be back.

What does a passing level of service person do? Not call you, “Hon” or other terms of familiarity and show a level of good manners in general. Their hands etc are clean and their appearance is not frightening. (White gloves, as in the past, are not expected.) They can remember your order and check once during the meal if it is ok. They can pay attention to your table so when you signal they notice and come as soon as they can. If the owners gives them an unreasonable number of tables to look after because of a special situation, they can mention it, so you have more patience with the service.
Superior service is when they remember what you like and offer a welcoming smile. Or they do something above and beyond from what is generally done.

We have come across some scary looking restaurant employees in last few years. A face full of metal does not give me ideas of returning anytime soon.