Not mentioning the automatic gratuity
Since saying, “That’ll be $11, tip included” is kind of a mouthful -- and will undoubtedly need to be repeated multiple times over blaring renditions of “Glory Days” -- often the bartender will neglect to tell you that the price includes the tip. If you pay cash, ask. If it’s on a card, look to see if there’s a line that says: “ADDITIONAL gratuity.” Feel free to tip twice, but just know you’re doing it.
Icing your drink down
Ice is a bartender’s best friend. Oh, you think that gin and tonic you just ordered was a heavy pour? Nope, it’s just that your glass is mostly frozen water and the taste of a strong drink comes through as a result. And thinking he just did you a solid, you tip accordingly.