Stupidly had a ham arms race -- somewhat dippy! (3,2,1,5,4)
I believe the answer is:
mad as a march hare
'somewhat dippy' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'stupidly had a ham arms race' is the wordplay.
'stupidly' indicates an anagram (a stupid ordering of the letters).
'had'+'a'+'ham'+'arms'+'race'='hadahamarmsrace'
'hadahamarmsrace' anagrammed gives 'MAD AS A MARCH HARE'.
Can you help me to learn more?
(Other definitions for mad as a march hare that I've seen before include "Out to lunch" , "Unstable" , "like a Tea Party member?" , "Crazy" , "Behaving excitably and unpredictably (3,2,1,5,4)" .)