That? That's what Crowley wants. Smiles like that. They've been too hidden, too much not to smile about. Crowley would do anything to let the angel just be his stupidly happy self, no matter what idiotic situation that ended him up in. Though, really, this situation was more dangerous and impossible than just idiotic, but Crowley did end up in his fair share of idiotic situations because of Aziraphale.

"We can take a taxi," Crowley suggests. "More likely to get lost in the crowd of cars, than just two people walking along the street."