I think tipping post-tax is part of the longer term inflation of tipping. Once 10% pre-tax was the acceptable tip, then 15% during the 90s, and now it has drift

I think tipping post-tax is part of the longer term inflation of tipping. Once 10% pre-tax was the acceptable tip, then 15% during the 90s, and now it has drifted to 18%, 20% and possibly soon above. Somewhere during that drift it went from being pre-tax to sometimes, and even most of the time, post-tax. All this despite it being a percentage of cost and thus scaling with the price of goods naturally.