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1.
It's about smiling. Ear-to-ear smile or grin is when you have a very broad and generous smile. Such a smile when each corner of your mouth is by each of your ears.
Explain to me why you don't have an ear-to-ear grin right now.
by Mr. Peagram March 08, 2012
 
2.
a cut from one ear to the mouth to the other ear, in other words a chelsea smile
the only way you'll see me smile is if you cut me ear to ear
by B-ri Myrders June 24, 2010