Disclaimer: Playing with toys that aren't mine.

Role Reversal

The bell on the door startled Aziraphale; he had not been expecting anyone today. He enjoyed Hallowe'en; customers were rare at best and children had such vivid imaginations. Plus, he quite enjoyed giving apples to the tykes(1).
Leaving his cocoa and much-loved book on the table, he walked into the front-- only to stop short. Aziraphale heard himself make funny noises in the back of his throat(2).
The intruder grinned.
"You like my costume, angel?" The demon asked, gesturing to his white suit, fake feathered wings, and plastic halo(3).
"Ahh... it's, hmm, very... sacrilegious, my dear," Aziraphale spluttered.
"That's what I hoped you'd say," Crowley murmured, and his grin, if anything, grew wider as he sauntered closer(4).
"Er," was all Aziraphale could get out before the almost-angel reached him...

GOGOGOGOGOGOGOGOGOGOGO

1: As an angel, he was wired to mistake glares of disdain for looks of gratitude. It made the job infinitely easier.
2: Imagine a cat coughing up a hairball made of indignation and disbelief.
3: Crowley had deeply considered a fake harp, but ended up not getting one because of the effort it would have taken to carry it around. He forgot to take into effect the bonus of being able to use it as a melee weapon.
4. It was more like approach with undemonlike nervousness, but don't tell Crowley.