John S. Farmer, Slang and its analogues past and present…
“ To fly off the handle, verb. phr. (American pioneer) .—To lose temper; to fail of a promise; to jilt; to die; also to slip off the handle (q.v.) ; to disappoint in any way. [In pioneer life for an axe to part company with its handle is a serious trial to temper and patience.] 1843–4. Haliburton, The Attaché. You never see such a crotchical old critter as he is. He flies right off the handle for nothing. ”
