According to this source via wiktionary, it's '[p]ossibly from a contraction of "grinning like a ’possum eating shit."'
I figured it came from a similar expression like "happier than a pig in shit" implying the person is happy about something they really shouldn't be happy about.
Huh, I always assumed it was referring to dogs eating cat shit.
Hm that kinda makes some sense. I have to wonder who ever saw a possum do that though. They aren’t much for being seen :)
If you lived in the country before TV, internet, gaming, or even electricity, you would probably have seen a lot more possums especially when you're hunting them for tomorrow's dinner.
I always figured it was meant to describe the kind of person who could sit and happily eat an entire plate of shit, and yet still think they've got things more figured out than anyone else.
According to urbandictionary, if someone is shit eating, it means "To be exceptionally smug, full of oneself."
I guess, it's a type of grin that makes someone assume the person is like that.
I know what it means. I don’t know what it has to do with consuming feces.
The are so into and proud of themselves that if they were to shit right now, they would eat it.
Someone saw my sci-show lizard post
A smile where the person is so full of it that you want them to "eat shit" (you hate it)
Because when your boss is doling out shit for everyone to digest, everyone sits there with a wide smile on their face to show how impressed they are with boss's fecal dissemination talent.
