Faunch: verb, meaning to rage and storm, to fight against fate. "Faunching at the bit" implies waiting in nervous agitation and impatience, like a wild horse that is fighting against a harness. Probably derives from Irish "fonn taodach" - to quote Daniel Cassidy's book, "How the Irish Invented Slang" (p.139) "an impulsive frame of mind, jittery excitation, a fierce humor", taodach meaning "excited, fidgety, quick-tempered." (Cassidy's entry was not defining "faunch", but "fantod." I made the leap myself.
I was faunching at the bit to drive my uncle's new Mustang.