S5 E3 - Free To Be You And Me: Dean taking Cas into a brothel
on YouTube, brothel stuff starts at 4:03
Castiel: "This is a den of iniquity. I should not be here."
They're just happy and chilling out and Dean's trying to be helpful and Cas is being really, really awkward and they're both sorta having a good time and it's all nice and there's laughter and backslapping and everything.