No, they kept me waiting 15 minutes without a huge fridge.
Bastard. 
Yes! Food brought to your table, food brought to your door. Tip.
At a sit-down restaurant, I tip the traditional 15% of the pre-tax total, rounded up to the next dollar if I’m paying with cash. (No idea why so many people say 20% nowadays.) I’ve never tipped anyone else, and I definitely won’t drop anything into the tip jars that have become common at fast-food places.
Do you never get a pizza delivered? Tell me you tip the pizza guy. (I was the pizza guy. This is important.)
It’s important for the consumer too. Getting a reputation for a being a non-tipper for delivered pizza may get you extra free toppings.
Are you talking to me?
My wife does the online ordering. I think she adds a tip when she gives them the credit card number.
We had a regular delivery customer who not only never tipped, but demanded every penny of change. Every time, and she was a regular. If the pizza was $19.95, and she handed you a $20, you better have five cents for her.
Once, in a cold Chicago winter, the owner of the joint boxed up her order, and I put it in the insulated bag. I brought it out to my car and headed down the road. (I didn’t “add” anything to the pizza but cold air. Really cold air.) I took the pizza box out of the insulated bag, opened my passenger window, opened the box, and held it near the open window till I got near the customers house. A few blocks from her house I closed the box, closed my window, and put the near frozen pizza back into the insulated bag. We did the usual exchange where I gave her every penny of her change back, and I headed back to the pizza place.
When I got there, the boss was on the phone with an angry customer who was delivered a cold pizza. He was dumbfounded and swore to her that he himself took this pie out of a pizza oven not five minutes ago, and there was no possible way that her pizza was as cold as she claimed.
Oh, it was that cold. It was very cold.
You might be thinking that’s the message you’re sending but that’s not the message received. Most waitstaff who get a poor tip just think the customer was a cheapskate rather than looking inward to figure out how they could improve in the future. Don’t get me wrong, if you’re getting bad service there’s nothing wrong with not tipping, but you’re not really sending a message that other people are going to understand.
Sure, no doubt you’re right, but I don’t think I particularly care about that distinction. I’m not seeking to put the world to rights, I am just paying them what their service was worth. If they choose to pay as little attention to learning from that as they paid to serving me, that’s up to them. I’m probably not going back anyway.
If I’m at a bar, I usually tip a relatively large amount for my first drink. I find that I don’t have to wait long for subsequent orders. I tip a more standard amount on the subsequent orders. This is one of the very few times you can tip ahead, so to speak.
This is one that gets me. I understand a masseuse at a hotel spa for relaxation getting a tip, but if my back is acting up I go to a Registered Massage Therapist I’m not tipping. I wouldn’t tip my physiotherapist either.
Yeah, I don’t think I would either. I’m sure my insurance is adding a big hefty tip, right?! 
When I visited Ireland with my mom some years back, at the first restaurant we stopped at, she asked the waiter what the local tipping customs were. He said “Oh, I always just recommend that people follow whatever the custom is back where they’re from”.
Heh, heh, heh … now you’re just trying to get me shot in the street.
Does that mean that if they are fleeing, having successfully completed their robbery, you should expect a tip if you hold the door open for them?
They spit in everyone’s soup just in case.
Thank you all.
Very helpful.
In a bar I run a tab. They know me and know I’ll be tipping them well and they usually “forget” to charge me for a round.
Just to clarify because the OP is visiting from a foreign country where tipping customs are different:
Tipping (usually 20%) in a restaurant or bar is NOT optional. Yes, technically you can leave a zero tip and there won’t be any real consequences, but you will look like a cheap asshole.
I don’t want to get into a philosophical discussion on whether restaurant tipping is right and just. There are plenty of Americans who will argue that point. And it’s a stupid one that is not going to be settled by the end of your meal. In the United States, the custom is to tip 20% and the wait staff is depending on those tips. All refusing to tip does is short change people doing their job and makes you look like a jerk.
So bottom line, when you go to eat in a restaurant, assume you are going to pay 20% more than the price on the menu and that’s just the cost of doing business. If you can’t afford that don’t eat there.