Came from HEE HAW!!! Roy Clark would say, "I'm a pickin'." and he'd play the banjo...
Buck Owens would say, "...and I'm a Grinnin'." Then he'd play the guitar...
It was a segment of the Country weekly tv Show "HEE HAW"...
Pete, I'm gonna try again, My definition of it is when Lathan and whoever else starts playing and singing, I go to grinning. Hope you will join us this summer around the motel pool or at one of the rooms if it rains. MVB ES