that's why I made that crack to Glaston about being impious.
And, yes, asebia was regarded -- by the radical democrats who voted to execute Socrates -- as one of the ill effects that often came from "sophists," the traveling teachers of rhetoric. That's precisely where Plato is coming from in the Apology when he has Socrates define the charge: "There is a clever man called Socrates who has theories about the heavens and has investigated everything below the earth, and can make the weaker argument defeat the stronger."
What I meant about "vague concepts" was not that impiety or sophistry are in some ontological sense hard to define. I meant specifically that Athenian law didn't define the crime of "asebia," the way modern legal systems would, so that asebia ended up being whatever the voting jury wanted to make of it -- and being a sophist was something they thought could easily entail impiety.
In any case: Jeez, can't a guy make a Socrates joke without someone jumping down his throat?