Cool! Far out!
Want to use twentieth century expressions in your FIRPER? Be my guest. - Jonah
Ephraim Anderson of the First Missouri Brigade wrote of an incident that occured in June of 1863 while he and his pards were in Vicksburg: "There was a considerable quantity of rice in the town, owned by a private party, from whom we were in the habit of purchasing a supply to fill out our rations; and one morning, a pot of it having been boiled, several of the boys were sitting round eating it, When John Hanger's spoon was struck while just in the act of putting it into his mouth, by a small piece of shell, which tore a hole through the spoon and splattered the rice all over his face. John quietly observed ‘That was cool,' and continued to finish his breakfast." From Memoirs of the First Missouri Confederate Brigade, by Ephraim Anderson, 1868.
(By the way, the term "far out" was in use as early as the 1890's, and was used by Stephen Crane in his Maggie--A Girl of the Streets.)