chew the fat/rag, to

To converse, or to chatter in informal fashion. In Great Britain chewing the rag originally (late nineteenth century) was a col- loquial term for complaining or grumbling, although one source holds it was

an army term for persisting in an argument. Another source reports that the rag in question was a piece of cloth used when soldiers ran out of tobacco. Chewing the fat, more common in America, may have meant chewing on salt pork  or  fatback  when  supplies  were  low. Today  both  are  colloquial  clichés that simply mean talking in a relaxed manner.