It’s not a smirk, right, because those are done with the mouth closed?
Is it a peevish smile?
Or is it a wide-open lopsided smile/grimace as if one were being forced to eat a turd and act as if he or she liked it?
Don’t tell me this one’s been done already!
Thanks
Q
Now, I’m not telling you that it’s already been done. I’m just posting a couple of links.
[SEG] 
[/SEG]
I knew it!
Never one to shirk a challenge - my friend Johnny L A!
Quasi
PS to Damsel: I thought those examples below def #2 were hilarious, thanks!
Just my natural reaction when someone tells me ‘Don’t’. 
I guess Ms. Manners would call it “a coprophagic smile”?
Oh, and John? In one of those 2 links you sent me, I noted the date was 2000, same year I joined.
Don’t know how that’s significant or relates, just thought I’d mention it.
Q
I have only ever seen the term used once, and that was attached to a picture in “Hollywood Babylon”.
The way it was explained to me: when your boss tells you to do something stupid, you have to be able to control your emotions, do what he/she tells you to do, and do it with a positive attitude. This is called “eating shit with a smile.” This would probably match the urban dictionary’s #2.
However, in my experience, it is probably closer to #1: a grin that doesn’t reflect what’s happening around the grinner.
I always associate it with inappropriate humor.
A lady with lipstick on her teeth or toilet paper stuck to her dress. A person trips and almost falls. Someone steps in dog poop.
Anything that catches your eye and makes you smile while your trying not to laugh. You know it’s really not funny, and that makes you smile all the wider. 
If you’re caught smiling, then it irritates the other person and they say “wipe that …” off your face.
That smile you get when the guy tailgating you passes you on a double yellow line and then turns left… and the person behind him is a cop.
In my younger days (1970s), it was used according to definition #1… usually in reference to someone who had smoked a large quantity of weed.
Watch almost any episode of USA’s “Burn Notice” and, at some point, the Michael Westin character will give what can only be described as a shit-eating grin.
As I first encountered the term, it was more like definition 1. It’s sort of like the silent version of a conspiratorial or self-satisfied chuckle. FTR this was in National Lampoon’s magazine version of Animal House. As Bluto and D-Day pulled the test answer sheet out of the trash, Chip Diller and Neidermeyer looked on with shit-eating grins, because they’d tricked them by planting the wrong answer sheet.
That’s the way I always understood it. Someone does something sneaky and are pleased with themselves for having gotten away with it=shit eatin’ grin. When I was in high school one of my friends mom used it a lot, as in “What’s with the shit eatin’ grins? What are you two up to?”
(Smoking pot mostly)
I’ve heard it used in both senses.
