Very eccentric (4)
(Other definitions for mad as a march hare that I've seen before include "Out to lunch" , "Behaving excitably and unpredictably (3,2,1,5,4)" , "like a Tea Party member?" , "Crazy" , "Unstable" .)
(Other definitions for zany that I've seen before include "Madcap, like a clown" , "Comically eccentric" , "Crazy" , "old assistant clown" , "Absurd" .)