Green’s Dictionary of Slang

hammerheaded adj.

stupid, stubborn.

1597		G. Harvey Trimming of Thomas Nashe B4: I thinke that halfe a yeeres study did not bring it out of thy dunsticall hammer-headed scalpe.
1600		Nashe Summer’s Last Will and Testament in Works VI (1883–4) 169: A number of rude Vulcans, unweldy speakers, hammer-headed clowns.
1890		Sheffield Dly Teleg. 20 May 5/5: Hopeless, hammer-headed obstruction is the short history of this evening’s sitting after question time.
1917		Van Loan ‘Egyptian Corn’ Old Man Curry 223: You great big hammer-headed lobster, what have you got to say for yourself?
1970		in DARE.
1986		Plus Sept. 14: I love my husband, but he’s as hardheaded as a mule [...] An ornery, balky, hammer-headed mule! [HDAS].