dumb bunny
A stupid, silly, or naïve person, usually used in an affectionate or endearing (if condescending) manner. Ah, don't mind him; he's just a dumb bunny, but he is harmless. Oh, my darling! You are the sweetest dumb bunny I've ever known.
dumb bunny
A stupid person, as in She was a bit of a dumb bunny but very nice. This expression implies some toleration or endearment of the person. [c. 1920]
dumb bunny
n. a stupid person; an oaf. Who’s the dumb bunny in the double-knits?