Aziraphale and Crowley were sitting in the Ritz, enjoying a nice midafternoon cup of tea, when their peace was shattered by the excited squeals of a young woman with a man kneeling at her feet.
Apparently, he'd proposed.
Crowley's lip curled, and he snickered quietly as the young man tried to stand up, only for his shoes to have been somehow knotted together. Aziraphale swatted at him, but there was a slight smile tugging at the corner of his mouth. Crowley knew the couple had just been given some sort of boon- and when the manager came over, declared that their meal was on the house, and offered to host the reception dinner, he knew exactly whose fault it was.
He didn't bother changing it- the manager would get an earful from corporate, and take it out on his staff, who would take it out on the patrons, and slowly spread the irritation and anger around through central London. Crowley loved it when things worked out like that.
He took another sip of tea, and turned back to Aziraphale. "What I don't get, is why bother tying the knot at all?"
"Hmm?"
"The whole business with the priest and the vows- half the people getting married by a priest aren't religious at all, never mind enough to want their union to be blessed by Him."
"Tradition is important to humans- it's reassuring. And in an endeavor as complicated and emotionally perilous as marriage, I think anyone would want the approval of a higher power."
"S'not like He ever blessed humans before- Adam and Eve got the boot for it." At this point, Crowley's tea was half empty, and upon realizing this, it suddenly became full again- half tea and half whiskey, as Crowley expected it to be.
"Hmm. Well, there was the business with- but then, that was His son. And perhaps, the humans merely feel more comfortable, having exchanged promises for protection, and security, and mutual aid?"
"Why would anyone want that? How could you trust that they wouldn't stab you in the back, after they promised?"
"Well, if you're looking at it that way, you're sitting for tea, discussing human traditions with a soldier of God. Our Arrangement is very much like an exchange of marriage vows."
Crowley opened his mouth quickly- about to argue the angel's point. He stops, thinks for a moment, and shuts his mouth. Behind the sunglasses, Aziraphale can see the Serpent's eyes, flicking rapidly over him, and coming to rest on the table, staring hard as though to force it to give up an answer, any answer that could refute the point Aziraphale had just made.
Finally, he said: "I'm not buying you a ring."
Hiding a smug smile behind his teacup, he took a long sip. "I wouldn't dream of it, my dear."