Before Diamond, I had primarily stayed only in PHs domestically and Hyatts internationally. During my first visit to a US Club lounge, I had no idea they had an honor bar. I poured a usual glass of champagne assuming it was complimentary, as it had always been. An attendant brought me a honor bar slip.

So, I just filled it out. Still can't get used to this concept and find it very peculiar.

PS - For instance, in GH HK, they not only allow free flowing Ruinart, but refill your glass throughout the evening.