Here is a winning answer: "If you say so."
I don't know...... Personally, I've always used that expression to convey "I'll grant reasonable doubt in this situation" or even" I recognize your knowlege, and my own lack, in this area. I won't even risk a sophist response. However, proceed with caution.". The key word being "If"
When I wish to convey " Look, your full of crap with that poor, juvinile, and transparent attempt at diversion, shut the f up and stick to the subject at hand.Consider this a tacit warning." ,AND I deem dignity, and civility remain appropriate,I often use "So you say.(cold, and rightious condecention is the essential tone!)However, concerning...."(fill in blank-immidiately going back to subject at hand, without pause for breath)
I realize it's a subtle distinction and ,of course, my own bend. I find "So you say." equally effective as a simple ender to baited discussion, provided it's my final word.