Okay. The expression “shit-eating grin.” Where the hell did it come from? I know I wouldn’t be grinning under the circumstances…so why has term come to connote an extremely, if not excessively, happy person?
I think that comes from the phrase, “grinning like a possum eating shit.”
Well it’s been brought up before without an answer…
SDMB Shit Eating Grin
Honestly, I have no idea. But my personal interpretation has always been that it is supposed to conjure up the expression of someone trying to eat the substance in question while getting as little of it in contact with his/her mouth as possible.
My WAG is more along the lines of someone grinning so broadly and seeming so happy, that eating feces would be no big thing for them.
Or maybe it falls somewhere along the lines of grinning so stupidly because there is no other choice. The context I’ve heard it used in is often the exact situation where one would not be expected to be grinning, and the big and wide grin is just an absurd reaction.