Human Cas trying different drinks for the first time (Victorian child inspired):
Water
*frowns* "It tastes like time..."
Dean: So you don't like it? Cause you kinda need that to-
Cas: No. It's great. (and he means it)
Milk
Cas: "You know, adult humans really shouldn't be drinking this. This would have been unheard of in the 18th century, and I really don't understand the appeal of cow secretions-"
Dean: *plugs his ears* Ahhh... enough. I do not consent to hearing those words.
Sam: You know, he's not wrong! Get this-
Dean: Kindly, shut! up!
[Dean slides the glass forward]
Try the milk. : )
Cas: *sighs and tales a sip* I am not a calf. This is weird. I feel gross, Dean.
Dean: Stop being so dramatic! This is why you're trying everything now, so you don't embarrass us in public. Come on, it ain't that bad.
[Cas then spends half an hour on the toilet. He is apparently lactose intolerant.]
Diet Coke
Cas: [Wearily] Is this dairy free?
Dean: It's diet-friggen-coke, Cas. It's dairy free. It's also sugar free! Because someone [he glares at Sam] has a bad taste in pop. Real honest sugar is probably better for you than this junk.
Cas: Agreed. The fact that it's sugar free does by no means make cocaine good for you. It's actually quite concerning that you boys drink this. I think we should do an "intervention."
Dean:
Sam:
Cas: Does 6pm tomorrow work for you two? I'll find some folding chairs and arrange them in a circle.
[They never could get Cas to drink diet Coke, because why is it still called Coke, if there's not cocaine in it? and that's false advertising, which I also do not condone.]
...........................................................
If people enjoy this one, I'll take suggestions for other foods for Cas to try
[Sam, Dean and Cas are staying in some house temporarily while on a hunt]
Cas: There's a female woman at the door
Dean: (at Sam) Wh- why is he saying that? (Turns to Cas) Why are you saying that?
Cas looks at Dean blankly and motions to the door.
Sam looks at his watch as the doorbell rings.
Sam: Ooooh wait, that's probably for me.
Dean: (confusion)
Sam opens the door and accepts a package from a mail woman.
Dean and Cas look at each other
Dean: Wait... When we get deliveries, you're... You're thinking it's called the MALE-MAN!?
Dean doubles over, laughing
Dean: AND SINCE IT WAS A LADY YOU ASSUMED IT WOULD BE A FEMALE WOMAN!?
Castiel looks extremely confused
Cas: that's what you said the other day, though, I know I heard you right? Male man???
Sam: (sets down with his package, pointing at it and smiling) Mail, m a i l.
Dean is positively howling in the background.