DP loves a good argument just for the fun of it, when he's a bit bored. Me, not so much. He sometimes makes statements that I know he doesn't even believe, he's just aware it's the opposite to my position and is trying to set up a little argument for entertainment. I can now shut him down in a few seconds in a way that makes it impossible for him to continue and rather satisfyingly leaves him turning himself inside out with frustration that I'm refusing to play the game.
Him : that wall used to be yellow.
Me: Hmm? No, it was purple.
Him: No, don't you remember, that wall used to be yellow.
Me: (realising what's going on here) Mmmm? If you say so.
Him: (trying to head me off) Yellow, it was yellow, I said it was yellow.
Me: Yes I heard you. Ok, if you say so.
Him: Do you really think it was yellow?
Me: If you say so.
Him: errrrrrr. (getting frustrated that the game isn't going to happen) Why won't you argue with me!
You have to do it in a matter of fact, uninterested 'yes, I'm just humouring you' tone of voice.
They can't argue with someone who is agreeing with them, on the surface. But it's a way of agreeing while showing that actually you don't agree (or you'd be saying, yes, you are right, it was yellow wasn't it) but that it's such a petty little thing you can't be bothered to discuss it with them, and fine, if they want to think it was yellow, go ahead, knock yourself out, I don't really care either way. They don't get that 'win' satisfaction from you, and you don't get dragged into a waste of time argument.
I seem to remember a scene in Taming of the Shrew
where Kate does that to Petruchio.
Text: "Yes, dear, whatever you say."
Subtext: "Are you done yet?"