I Did Not Like the hooker bit - show, your issues are showing again.

However,

I think when the devil says, "I will never lie to you. I will never trick you", he is fucking LYING.

I disagree. The tricking part is perhaps more in question, but the truth is often a much more powerful weapon than lies. And hasn't that been a plot point somewhere else (in other fiction) - that the Devil doesn't actually lie?

He/she was pretty truthful to Nick when convincing him to become a vessel. Plus, I thought that wide-eyed gleeful "Hey, guess what—I'm the Devil!" delivery was way creepier than any of the threats and deceptions we've seen from demons.

The Devil isn't going to be about lying, but about manipulation. Nothing he says to Sam to try to convince him is going to be untrue, it's just going to be a really narrow interpretation of fact that is designed to get him what he wants.

I thought it was funny, so.

Which I guess brings me back to me not getting that part, since I obviously didn't, and it makes me feel like I am missing something.

I just found it very Dean-like that this would be his plan for a last night on earth, even if it was an angel's. Also Cas's sort of blind faith in taking Dean's advice. It was absurd, which Dean often is. And doomed to probable failure, which Dean's plans (of this nature) sometimes are. He can carry out a hunt with amazing precision, and he's a lot smarter than he gets credit for, but his interpersonal skills need a lot of help.

So ... it was amusing to watch, for me.

It was all just so absurd. Cas is so intractably innocent. Dean tried to corrupt an angel and instead the brothel's bouncers start after them. I think for Dean it was a long-shot that Cas would have "seeded" Chastity's cloud, but it might have reminded him of how he and Sam once were. It was a pretty telling moment.

The "Dayenu" line had me falling out of the chair.

I felt very uncomfortable during the bordello stuff. I don't think even Dean would consider getting an angel laid on his last night alive as a good thing. Knowing Castiel, and seeing his reactions to other things and situations, I doubt that even Dean would have thought for a second that was something Castiel would want for himself.

It did hurt, watching Dean try to shoehorn Castiel into the Sam-shaped hole in his life. And I think his comment about being free of his family feeling good may have been almost 100% sincere. His further comment about feeling great being alone at last? Sheer bravado.

The Rafael (Raphael?) actor was wonderful--amazing voice. It's difficult to convey power and powerful emotion from a static position, but he was just fabulous.

Sam broke me. JP is blazing through Sam's storyline and pulling unbelievable depth and subtlety out of his actor's bag of technique. The Lucifer actor (Mark Pelligrino?) is against type, but man, is he bringing this version of the Lightbringer to the screen. So subtle, so facile, so sympathetic. And it's working on Sam, poor man, who try hard as he might, can't succeed, can't resist, can't pull away from inevitability no matter how much he wants to, how hard he tries. Oh, Sam.

For Dean to say, "I'm happy"... Honestly, I don't think he knows what that means. Being unburdened isn't the same thing as being happy.

How long was it before the fanfic hit the interwebs concerning what Dean did to make sure Castiel wouldn't die a virgin post-getting chased out of the bordello?

The author is probably having it beta-read now.