You just need to learn to have fun with it.

Order something that's not an actual item. Make it really complicated, long, convoluted, and change your mind a couple of times in there. Say it super fast. Then at the end, tack on, "if you don't have that I'll just take a medium coffee".

Guess what you're gonna get? A cup of medium coffee. Without any drama whatsoever or any more questions asked.

Alternately, you could do what my dad does. He orders whatever the cashier's favorite is. For some reason this completely flummoxes them. So he says, "Or a medium coffee".

99 times out of 100 he ends up with a medium coffee.

Penguin, I'm starting to get the feeling that you lack or have lost some basic skills in public navigation. Rough pandemic?