A few years ago the patron ahead of me at the Centurion Lounge in Las Vegas tipped the bartender $20 (LAS revolves around tipping, when one stays in LAS publications are left in your room listing dining, entertainment etc. options, one page is frequently devoted to "suggested tips".)
AA Flagship lounges are open bar. Many years ago DL Crown Rooms (called SC today) were also open bar = no tipping.
Pre Covid, in the late afternoon-evening, at JFK a rolling cart dispensed drinks, did the cart agent expect a tip?
Aren't tips supposed to be (totally) voluntary? [A few restaurants add stated tip amounts to meals, generally parties of 10+ have required tips--but that feature is stated "up front."]