rough as a cob 

In earlier times, a corncob was used by some for personal hygiene concluding a visit to the outhouse. To say that one is "rough as a cob" is to note their abrasive manner, or unpolished style of approach usually in regard to communications or actions.

You know John ain’t got no smarts, he’s as rough as a cob.

rough as a cob by NC get it right September 28, 2006

rough as a cob 

Mighty unpleasant.

From the rough surface of a corn cob used to wipe one's backside.

"Hey Elmore, the wheel done fell off mah baler."

"Oh man, Ermal, that's rough as a cob."

rough as a cob by The Wog Whomper May 1, 2005