Interpreting your quote - "why are you being a poophead?"
OK. For the record, the "why" is rather misleading. You don't care "why", have no interest in it. You are simply intimating there is a "poophead" in the dialogue, and that's about it.
Or you could be asking why someone is being a bit fractious. Again, why isn't an issue, really. It's just pointing out that someone is being (unpleasantly) difficult, along with an implied wish they'd stop and be more agreeable.
Those are my interpretations. Neither is a ditch in which I'd like to die. On the other hand I suspect they are fairly accurate.
I hope this helps.
Arf