adjective

unable to make intelligent decisions or judgements; foolish or stupid.

stupid,idiotic,moronic,imbecilic,foolish,half-baked,half-witted,dim-witted,witless,dunce-like,doltish,cretinous,empty-headed,vacuous,vapid,dumb,dim,dopey,dozy,birdbrained,pea-brained,fat-headed,lamebrained,chuckleheaded,dunderheaded,wooden-headed,muttonheaded,boneheaded,crazy,mental,nuts,nutty,cracked,cuckoo,bonkers,dippy,daft,potty,barmy,batty,dotty,crackers,dumb-ass