To be perfectly fair, human beings can't pick up on sarcasm reliably: or at the very least it seems to be cultural/contextual.
Australians/brits consistently bemoan the inability of Americans to understand deadpan and sarcasm.
And I'm even reminded of one of my European friends (from Austria) bemoaning conversations with Germans along the lines of:
Austrian: "could you be any more condescending!?" German: "yes I could be more condescending."...blank stare.