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Sometimes shit-eating grin.

(1) n. A shit eating grin is a very wide and, to the outside observer, stupid looking grin, usually showing smugness, self-satisfaction, or inner humor. The term is most often seen in the expression "Wipe that shit eating grin off your face!", usually said by the aforementioned outside observer. This observer-based definition makes "shit eating grin" the negative counterpart to "You look like the cat who ate the canary." While the two expressions describe the same grin, they have very different connotations. This definition has nothing to do with the term "shit eater".

(2) n. Someone donning a forced smile in an uncomfortable, embarassing, or compromising situation could be said to have a shit eating grin. Because an uncomfortable situation is much more closely related to "eating shit" than smugness, it is plausible to assume that this is the first definition, although far from the most common, and that the above definition is a result of drift from this one.

Both of these uses are documented in the Oxford English Dictionary no earlier than 1957.
(1) Upon telling Elaine he knew a secret, Jerry donned a shit eating grin and refused to reveal it.

(2) Forced to admit defeat, the politician managed a shit eating grin as he called for and end to "bipartisan rhetoric".
by GuildNavigator84 February 08, 2006
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"You got the promotion! I knew there was a reason for that shit-eating grin."
by AbnormalBoy September 02, 2004
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A huge wide grin worn by a complete asshole after he just fucked you over. See NHL player Jarkko Ruutu
Left D "Ruutu hit me in the groin last shift, what a dick"
Right D: "Yea that shit eating grin on his face makes me want to wipe it off with my skate blade"
by Scotty Bones09 April 07, 2011
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A)The grin on someone's face when they are trying not to smile but cant stop so they look like a total shithead.

called a shit eating grin because:

if you ate a piece of shit and you enjoyed it, you would naturally smile, but also try to hide that you enjoyed it at the same time, thus resulting in a "shit eating" grin.
"Wipe that shit eating grin off your face."

After John beat his friend Jim on a test, a shit eating grin came over him.

person 1 "Look at the size of that guys shit eating grin!"
person 2 "Man he looks retarded."
by Simmons12 August 01, 2006
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