Old manners, a formal affair, and perhaps simply a hint of fondness and a dash of excitement over the idea of attending a party together without having to make sure they aren't found by their former employers. Maybe it's just that Crowley's dress is lovely. It can be many things.

Aziraphale notes how much taller Crowley is in heels.

When they enter the party, it's quite clear that it isn't exactly all that of a formal affair - more of a juvenile attempt at one. But that's alright. There's just something about the mood in the air that makes it all very tolerable.

"What is that music?"