You tip because that’s how somebody makes their living. You don’t do it to prove something even though it certainly communicates something. You want to show that you are sympathetic to a bartender. Maybe a few dollars for a first drink and one for each drink after that (if it’s a low-key place). If it’s a more elevated setting then 20% remains a good guideline. You’re not paying for just the drink but for the time you’re spending there. If I’m in any setting where I sit at a table I will never tip less than five dollars (as in a diner, where the meal may be cheap).
