For those of you unfamiliar with the phrase, it’s more or less user as a sarcastic way of saying thanks for an act of generosity that isn’t so generous.
Me: “Hey, WTF happened to my burger?”
therealsope: “I was hungry so I ate it. But here, I saved you some pickle slices. I wasn’t going to eat them anyway, but you can have it.”
Me: “Well, that’s mighty white of you.”
What part of the phrase does the sarcasm modify, the white part and the implication that the man is fair or to the entire saying itself?