Why don’t restaurants pay living wages? I don’t know, but it’s customary not to do so. As long as they don’t, the wait staff are not the ones to take it out on. They probably work a lot harder for less per hour than you do.

In general, it’s not a good idea to bite the hands that feed you.

And where I’m from (philadelphia) anything less than 20% is the standard minimum for tipping.

Don’t go out with 10+ of your church buddies to a restaurant with only a moment’s notice and expect to be seated at a single, long table. Most restaurants offer a limited large group menu and encourage you to submit your orders beforehand. But if you arrive together, and insist on being sat together, expect things to take much longer and cut the server(s) a lot of slack.
If you are in a large party, don’t go crazy with the odd orders. Every raspberry lemonade or salad with extra Ranch dressing and no onions you order, you slow the server down just that much more, expecially when it comes to refills. “Tea refill? No problem! Let me just get this pitcher I made just for this table. Peach tea refill? That’ll be a minute, because I have to go back to the back, pour you a new tea, go to the bar, get the peach flavoring, mix it in and then bring it back out.”
If you’re in a large group, sit near the person paying your check. If you have to have separate checks and have to point to another table for people whom you’ll be paying for, you’ve just added 10-30 minutes to your overall time to sort all the checks out.
In a large group? Pay cash. It takes time to run the charge cards of 10 or 15 different people. Cash is good everywhere.
Don’t complain when one part of your large table receives their food before you. For example, let’s say you’re part of a table of 20 with 2 servers assigned. Each server can carry about 4 plates at one time. That means about 3 trips back and forth between the table and the kitchen. It’s going to take a little time.
Don’t pester the server with refill requests and requests for more rolls, etc. There will come a moment when he or she will ask, “Does anybody need anything?” That’s when you tell him or her you’d like more soft drink.
Finally, when the ticket comes, if you still feel you’ve received poor service, ask to speak to the service manager. Explain the problem. They may remove items from the ticket. They may not. Either way, tip a t least 10% on the remaining ticket. Especially on large groups. Your table is likely the only one they’ll have their entire evening. If you leave them nothing on a $200 ticket, they’ve lost the money they could have made taking other tables during the period they served you, plus they’ll have to tip out between $4 and $10 to bartenders and bussers, plus they’ll have taxes taken out of the $2.xx/hour wage they received for the night.

I don’t know a single server whose goal it is to provide poor service, so if you experienced poor service, things could be blamed on a slow kitchen, or they’re simply having a bad night (like everyone does from time to time) or maybe your table’s demands were a little over the top.

I’m not saying you have to tip 20% even when you receive poor service, but I am asking you to consider all of the circumstances and at least consider the effort your server(s) put forth in taking care of you.