When Pittsburgh diners receive poor service, they often complain to the restaurant. And many also share their complaints with me.

Over the past 16 months or so, I've received several hundred e-mails and phone calls voicing complaints about service, enough to get a good sense of the things diners most wish servers would stop (or start) doing.

At the same time, servers have their own share of complaints about diners. While it's true that diners are the paying customer and may have a right to complain, many servers don't make enough money to put up with the kinds of bad behavior they see far too frequently.

So here are the top pet peeves I've seen from the sides of the customers as well as the servers:

Diners hate it when servers:

1. Touch them.
Unless you're personal friends outside the restaurant, even a pat on the shoulder comes off as condescending at best and totally inappropriate at worst. Unless you're touching someone to keep them from falling or injuring themselves, keep your hands to yourself.

2. Clear one person's plate before everyone is finished.
It's part of a server's job to know the basic rules of service, and to know more than the basics if you're working at a fine dining restaurant. Some rules may be old-fashioned (such as always serving women before men), but ones based on common courtesy should never be ignored. Clearing plates early can make diners feel as if they've eaten too quickly or too slowly. It can also make diners feel as if the server is hovering over them. It is difficult to monitor a table so that one knows that a group is finished soon after they have, but acquiring these skills is an important part of becoming a good server.

3. Respond rudely to the use of coupons.
Especially during these tough economic times, no one should ever be made to feel bad for trying to save money. The restaurant gave out the coupon or participated in the promotion, which means that its staff must welcome that guest as they would any other. And if the guest has misunderstood the terms or if the coupon has expired, treat the guest with some compassion, rather than like an idiot or someone trying to get something undeserved. And diners, please remember that servers do just as much work when you pay with a coupon, and consider calculating your tip based on the full cost of the meal.

4. Decide or even imply that food allergies are just preferences.
If someone says he or she has an allergy, treat it as such. It may be obvious that they don't really have an allergy, but that doesn't mean their wishes should be ignored. Diners, see below for why you shouldn't pretend to have an allergy when you don't.

5. Decide that they don't need to bring change and disappear from view.
If a diner pays with cash, it's generally fine to ask politely if they need change. However, some diners may take offense, so you're probably better off just bringing change no matter what. A server should never, never count the money, calculate the tip percentage and decide that the diner must have meant to leave the change as a tip. Whether or not you agree with the practice, it's up to the diner to decide how much to leave, and taking the matter into your own hands is akin to adding a charge to their credit card without permission.

Servers hate it when diners:

1. Touch them.
Just as servers shouldn't touch diners, diners should never touch servers. Servers are not objects. You are not buying the right to flirt with them along with your dinner. Keep your hands (and your comments) to yourself.

2. Treat them if they don't exist.
When a server comes over to take your order, don't continue your conversation while they're standing there. Servers are trying to balance the needs of many diners, and it's not too much to ask that you pause for a moment, communicate, and then pick up your conversation when your server has accomplished his or her work. This goes double for people on their cell phones. If you need to use your phone, excuse yourself and go stand outside, in a discrete corner or in the restroom. Talking on your phone at the table is discourteous to your companions, your server and any other diners in earshot.

3. Make a complete mess.
Your server is not your maid. While diners obviously shouldn't worry about bread crumbs, accidental spills or the occasional dropped green bean, do not treat the table as your trash bin. Don't leave crumpled, used tissues, the detritus from your bag and the wrapping paper from your birthday gift for the server to clean up. At the very least, graciously apologize to your server for the mess, and if he or she responds graciously, increase the tip.

4. Eat 90 percent of a dish then try to send it back.
It's an acceptable practice to send a dish back in a restaurant if it was made improperly, but it should take just a couple of bites to determine that. If you've eaten more than half of the dish (and the dish consists of more than three bites), then you've forfeited your right to complain. Of course, if your server asks for your opinion, you can still say you didn't particularly like it. Just don't expect a replacement or a freebie.

5. Say they're allergic to something when really they just don't like it.
When you claim an allergy that doesn't exist (especially if you claim it inconsistently) you make it more difficult for diners with true allergies to get their point across. It should be enough at most restaurants that you don't like something. Try phrasing it as a request for help, rather than a demand: "This dish is appealing to me, but I don't like [your least favorite ingredient here]. Would it be possible to make this dish without it? And remember, it is a chef's prerogative to refuse to make substitutions. Chefs work hard to create dishes they're proud of, and if they can't vouch for a dish when changes are made, it's their prerogative not to serve it. If you can't find anything you like, it's your prerogative to go someplace else.