If I use a coupon, or there's a special on a meal at a restaurant, should I tip on the original price or the discounted price?

You always tip on the regular price before discounts. Generous people tip on the full price plus tax total.

Wait staff work hard and don't get paid at all well. Tip well Be kind.

origanal.. if ur into being generous to the cook

Tip on the  original  cost ALWAYS! Most tipped employees do not earn paychecks. In my neck of the woods restaurants only pay $2.13/hour. Then we are required to report our tips, which the IRS taxes you for, which is taken out of your check. It's very common to receive checks with zero value. And consistently recieving a paycheck at that rate is a sign something is very wrong, and your probably not feeding your family. Even worse, if you earn good tips, not only will you not receive a paycheck, but also the IRS will track the leftover taxes that your hourly wage didnt cover. When most of us get tax returns at the beginning of the year, servers often have to pay in to avoid audits and penalties. As a general rule of thumb, your server did the same amount of work and provided you with the same service you would have recieved at full cost. Why shouldn't they be compensated the same? You benefit from a cheaper meal, the business benefits by using your coupon to hook new customers, and the server often takes a loss. Tip your server adequately please. 

You tip on the total you have to pay at the cash register.

I tip on the full price.

Always tip on the original amount.

You can do it either way,I would  tip based on the original price.

It really doesn't matter, since it's usually such a small amount.  For example, if you saved $10, and you were going to tip 20%, that's $2.  The waiter isn't going to care one way or the other.  If the service was good, tip more.

Tip at the original price.

That all depends on if you're a pedantic diсk or not, like maybe if there's a discount that lowers the price to less than $10 and you have as $10-off coupon, when the bill comes back that the restaurant actually owes you money, you can say to the waiter, "Looks like you owe ME a tip, hammerhead."