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.