What is the proper etiquette for a querier who receives editorial comments and R&R from a literary agent, but after careful consideration, decides not to proceed with the revision? Polite email explaining why? No response? Ignore R&R and query the next book when ready? None of the above?
While "You're a dunderhead for suggesting this" is probably not the best choice, it's also true, even the polite version of that - "Thanks but no thanks"- isn't going to get you anywhere.
You're under no obligation to follow an agent's advice.
But no one, not even dunderheads, likes to hear our pearls of wisdom are being discarded as worthless trinkets.
Thus "thank you for your notes; I appreciate your time and insight" is all you need to say. That their insight made you realize they are idiots, can go unsaid. Or that you don't intend to implement their suggestions.
If, at some point in the future, the agent gets in touch to ask whatever happened to your retelling of Casino Royale with dogs,
that's when to say "I decided to go in a different direction." Unless they ask, you don't have to tell.
But just one more little trinket of wisdom: before you write off editorial comments and revision suggestions, let some time pass. Some of our advice is better after it sits awhile. Yanno, like novels.