If service was fucking fantastic
What you should tip: Whatever your heart desires
If your bartender has totally gone out of his or her way to make sure your time at the bar has been the absolute best, throw down the standard 20% to start, then add on however much extra you can spare, like your phone number. Just kidding, always tip in cash.
If service was fine and normal
What you should tip: $1-$2/drink at a regular joint, 20% of the total for a swankier spot
One or two singles will do for an average, respectful exchange of money for alcohol -- no special treatment, no drama, just efficient, cordial service. "$1 minimum per drink has always been the standard, but I've noticed an increase to $2 per drink over the past year," Karl says. Try to keep up, buddy.
If service was bad
What you should tip: 15-18%
"We all have bad days," says Karl, "so a little understanding goes a long way. Unless the bartender was racist or somehow violated your human rights. Then you should fucking leave. Just leave." A bad Yelp review might also be in order.