I was too stunned to say anything.
The bartenders there are consistently amazing. I don't even have to order a drink--I say hi, put my bag down at a seat, go to get my soup and the drink's waiting for me when I get back.
AC bartenders are great. It's rare to come across an inattentive or unfriendly one. I firmly believe that tipping preserves this experience.
It would've been hard for me to abstain from smartassery upon witnessing this woman's deed.