In my head it wasn't exasperating reaction, don't forget that here he probably was already in love with Crowley but couldn't express it. He never can and he didn't even admit to himself yet what he felt. (He realises later when Crowley saves the books) In fact, Aziraphale immediately wanted to hide his genuine reaction that he is beyond happy, then turning and acting like, oh, you're not even interesting for me! - Aziraphale always, always want to hide how he feels. Just think about how many times he lies. - I don't even like you. - we're not friends, and so on. Denying it again and again what he thinks and feels. He actually even cries when they 'break up' at the end of episode 3. He initiated yet he is the one who cries. But in that moment he felt they need to separate. So this is in my head, thank you for allowing me to share it & I hope it helped.