And that was not a sarcastic question. If you're feeling at all unsure about your ability to tell the difference between sarcasm and straightforward statements, learn all about the tests designed for just that.
There are multiple conditions that can wipe out, or greatly diminish, a person's ability to detect sarcasm. These include lesions on either side of the brain just "inside" the forehead, Alzheimer's disease, and certain kinds of autism. The question that researchers most often try to establish is, what else goes along with the sarcasm? It could be the ability to decipher subtext in a statement, or the ability to understand what a metaphor is, or the ability to comprehend something other than physical reality.
All of those concepts are part of a generalized mental ability called the "Theory of Mind." At a certain point of mental development, we get that what's in a person's mind, our own or someone else's, can be different from reality. People have desires, fantasies, plans, and knowledge — even erroneous knowledge. Most tests for sarcasm detection start with a pretest. A subject is shown that an object is hidden inside a box. They are then asked if their friend were to walk into the room, will that friend know where the object is hidden? The ability to understand that while the subject knows where the object is, their friend doesn't have the same knowledge, forms the basis of more specific functions.
One of which is recognizing that if a kid comes home with a bad score on a test and his mother says, "You're a genius, aren't you?" the mother actually means that he "isn't a genius at all." This is one of the questions on a basic sarcasm detection test given to kids with high-functioning autism. Some kids will just assume that the mother means exactly what she says. Subtle barbs are lost on some kids with high-functioning autism. They also don't understand what's happening when another boy, named Jiro, gets the sharp edge of his mother's tongue when she looks at her son's messy room and says, "Jiro always leaves his room in a tidy state." The test shows how very unpleasant it is to be around sarcastic and passive-aggressive people, provided you can understand sarcasm and passive-aggression. Even friends get some nagging in, asking a boy about to leave a messy room, "Are you leaving without tidying up?" This was a question designed to spot a kid's ability to spot indirect reproach.
Another sarcasm detection test pairs actors saying the lines like "you're working hard," out loud, sometimes sarcastically and sometimes normally. People with damaged brains, particularly with damage to the right prefrontal area of the brain, couldn't pair the sarcastic tone with the right situation. If someone said "you're working hard," the test subjects assumed it had to be pretty much what they were thinking... that is, unless they were thinking of phrases like "the grass is always greener on the other side of the fence." People damaged in the right prefrontal area understood this as metaphor. Those with damage to the left side of the same general area couldn't comprehend the phrase non-literally. They also had a tough time with sarcasm — although not as tough a time as those with damage on their right side.
That seems to be the way of most sarcasm tests. They're meant to not just discover an inability to detect sarcasm, but sound out exactly what is wrong with someone's understanding of the non-literal. Do they not understand irony? Do they not understand tone? Or do they just not understand that the world can appear, even in someone's mind, as anything but what it is?
[Via Understanding Sarcasm and Metaphor, Metaphor and Sarcasm Apprehension, Comprehension of Figurative Language]