1. Tipping incorrectly
Everyone loves getting great food at discounted prices, which is why restaurant deals on Groupon or all-you-can-eat specials are so popular. However, many people make the mistake of paying a tip based on the discounted total.
A cheap meal doesn't make your server's job any easier. Remember to calculate your 18% or 20% tip using the original pretax total, before the discount. (For example, if you got a $20 meal for only $10, the correct 20% tip would be $4, not $2.)
Face it: If your waiter had to go back and forth to your table five times to pick up plates because you were filling up on the all-you-can-eat pasta special, it makes sense to pay him a tip that reflects his efforts.