First they came for the 20% at Per Se, and I did not speak out, for I wasn't the person paying the tab.

Then they came for the 20% at Ruth's Chris, and I did not speak out, for I had gotten tipsy on cabernet.

Then they came for the 20% at Olive Garden, and I did not speak out, for I thought the server was attractive.

Then they came for the 20% at Intelligentsia, and I did not speak out, for the creeping norm of paying 20% had been established.

They they came for 20% of my internal organs --- and there was nobody left to speak for me.

If this is trying to be clever, it could use some work, and if there's a substantive point, I'm not seeing it.

The point is that your purported, self-glorifying norm asks one to pay the default PoS tip of everyone who demands or might demand it in the future, to say "yes" to all of them. Counter purchases, grocery stores, fast food, whatever.

Could you maybe consider that there might be better and more practical heuristics?

Ok, but I draw the line at movie ticket box office purchases. That far, and no further.

So, no substantive contributions to make?