“Sarcasm” isn’t exactly the right word; I think it is closer to a metaphor. Of course, when I wrote a letter to the editor correcting a misstatement by the Hartford Courant regarding Independence Party candidate Tom Scott in 1994, the paper substituted my correct word, “calumniate”, and replaced it with “slander”. First, there was no need to change my exact word. Second, I was writing about a written piece, so libel would be a better word to use than slander, which applies to spoken lies. Even J. Jonah Jameson knows the difference.
I thought Duh might suffice rather than the sarcasm tag.
I agree with you that ‘sarcasm’ isn’t exactly the right word here.