Were I the DM, I'd allow you to use it--and then you would see just how useful the feat is when a proxy or deity "deals with you as an obstacle" by sending you to meet the Great Unknown.
Not a lot of thought in this, really--Athar may be defiant, but they're not stupid.
Annoying yes, but that's about all it seems. It strikes me this is either going to be useless, abused, or simply on a meta-gaming level utterly annoying. Sure it may be cute the first few times you do it, but after that people might just start taking pot shots when they see you coming up the street.
And while the Athar may not believe in the power of the dieties, standing physically in front of one and annoying it DEFINATELY shouldn't be encouraged!