I hate this question....
Okay, don't get me wrong.
It only applies when I ask someone something, they answer then ask, "why?" right away.
For example, I would ask, "what are you doing Saturday?"
Then the response is, "Nothing, why?"
Okay, no big deal?
It really isn't but I *am* going to tell you why...you don't need to ask.
Guess it mainly bothers me because I'm *not* the type who ask why right away. I will let it be up to the person to tell me. If no reason is given, I just let it be.