Dear sweet lord. Your man landed with his arse in butter. Does he know this?

Source:

Indefensible

Is this a good thing or a bad thing? I mean, judging by the context, I’d think it was a good thing, as in “Damn your husband is one lucky son of a bitch” but I’m struggling to figure out how “arse in butter” became a slang phrase for a good occurrence.

(I mean, I’ve seen that Brando movie where they had the butter in the…but nevermind that.)

Anyway, I was just curious about the origin.