Is all sarcasm sin?
Sarcasm is defined as "witty language used to convey insults or scorn." Generally, sarcasm appears to be praise, often over the top, which actually conveys disapproval.
Sarcasm, considered by itself, is not sinful. It is a language technique that can get a person to sit up and take notice of what they are truly doing.
Solomon used it for teaching: "The lazy man is wiser in his own eyes than seven men who can answer sensibly" (Proverbs 26:16).
Elijah used sarcasm when dealing with the false prophets of Baal and Asheroth: "So they took the bull which was given them, and they prepared it, and called on the name of Baal from morning even till noon, saying, "O Baal, hear us!" But there was no voice; no one answered. Then they leaped about the altar which they had made. And so it was, at noon, that Elijah mocked them and said, "Cry aloud, for he is a god; either he is meditating, or he is busy, or he is on a journey, or perhaps he is sleeping and must be awakened." So they cried aloud, and cut themselves, as was their custom, with knives and lances, until the blood gushed out on them" (I Kings 18:26-28).
Paul used it to point out the false pride of the Corinthians: "We are fools for Christ's sake, but you are wise in Christ! We are weak, but you are strong! You are distinguished, but we are dishonored!" (I Corinthians 4:10).
Sarcasm can be used incorrectly when a rebuke is delivered when none is deserved. An example of that is Michal's rebuke of David: "Then David returned to bless his household. And Michal the daughter of Saul came out to meet David, and said, 'How glorious was the king of Israel today, uncovering himself today in the eyes of the maids of his servants, as one of the base fellows shamelessly uncovers himself!'" (II Samuel 6:20).