Green’s Dictionary of Slang

assheaded adj.

[ass n. (1)]

foolish, stupid.

[UK]More Confut. Barnes in Works VIII 736/1: Thys felowes folishe apishenesse, and al hys asseheded exclamacions [OED].
[UK]Three Ladies of London II: Come giue me my ladies gowne thou assheaded elfe.
[UK]Nashe Pierce Pennilesse 29: They are an arrogant Asse-headed people.
[UK]Douland Ornithop. Micrologus 65: Asse-headed ignorance [OED].
[US]W.H. Williams Wreck II i: You pauper-fed, ass-headed, bull-faced beadle.