The Collaborative International Dictionary
boneheaded \bone"head*ed\ adj. very stupid; -- used of people or actions. [informal] -- bone"head*ed*ness, n.
Syn: blockheaded, fatheaded, loggerheaded, thick, thickheaded, thick-skulled, wooden-headed.
Wiktionary
n. The state or quality of being boneheaded.
Usage examples of "boneheadedness".
He also approved Dodge's silence on the matter of the tape left in his tape player, on Leaphorn's brief suspension, and on Jim Chee's boneheadedness.
Then, while she was still drunk but already beginning to feel the bite of a hangover, she’d drag Saucerhead Tharpe out of bed and try to con him into helping her manage some criminal enterprise noteworthy for its complete boneheadedness.
The cattle had to be treated, too, for the results of their boneheadedness, so out she went to three different farms, making sure each silly cow got her drench.