Shinola

Shinola is a brand of wax shoe polish available in the early- to mid-20th century. Its immortality in colloquial English comes from its being a dark, pasty, semisolid substance which is nonetheless distinct from shit (q.v.).

The colloquialism that brought unintended, seemingly permanent name recognition to the brand is, [He] doesn't know shit from Shinola. Implied is that shit and Shinola, while superficially similar, are quite different in effect when applied to shoes or carelessly stepped in. One who fails to distinguish one from the other is therefore notably unwise or of substandard mental ability. The phrase is famously uttered, and demonstrated, in the 1979 Carl Reiner film, The Jerk, starring Steve Martin.

Similar meaning can be found in the expression, He doesn't know his ass from his elbow, or the variant, He doesn't know his ass from a hole in the wall.

Recently a London-based film directing collective have adopted the name, with a spelling change: "Shynola." They have made music videos for the likes of Radiohead, Beck, Blur and Queens of the Stone Age.