I have to admit, I'm pretty bad at regional English. I always spot when someone spells like me, but I learnt to speak in so many places that I have no idea what's appropriate for where. If they say it in Jamaica, Canada, Britain, the Midwest or Cali, I'm probably good with it, and it takes some thinking to make sure it's not right for a generically American character.
(i.e. "proper button" does not twig anything for me at all. If Sam went off to university, well, that's all very sensible of him)
Dean might say "sew a button on properly," but very few Americans of his background use "proper" before a noun i.e. a "proper coat" or a "proper kitchen" or whatever. It's just not common.
I imagine if I wrote Whofic I'd inadvertently use a word or phrase that only yanks use.
Wow, that is indeed cool, Beverly!
I would go in, at least to shake someone's hand.
I've noticed several SPN fanfic writers using "ridiculous" as an adjective for physical objects like clothing and so forth in a way that strikes me as very British. I can see one of the Winchesters saying "this is ridiculous!" about a situation, but not using it as a descriptive word in that manner.
Rockstarpeach is killing me. KILLING me.
But I've decided how it's going to end, and I'm hanging tightly onto that.