Same I don't do it since it's against policy. Had a guy come in once ask for a Venti iced vanilla latte with extra vanilla sweet cream cold foam and to put it in a Trenta cup to fit the extra foam. I said I'm sorry I can't put it in a larger cup due to regulations. He shook his head and paid. Was about to walk away to wait then turned back and said, "Just so you know, you're the only store that won't do that. Everyone else will."
And I got so fucking frustrated in that moment. Like I was being called bad, being the bad store, cause EVERYONE ELSE would clearly do it. And I just gave in that one time and at the end slammed it down on the counter with a "Here it's in the Trenta, sorry for trying to stick to my companies guidelines like a good employee but here, have it your way." He took it and didn't even say thank you.