Cheerfully irresponsible (5-6)
I believe the answer is:
harum-scarum
'cheerfully irresponsible' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for harum-scarum that I've seen before include "Cheerfully irresponsible" , "Wild and reckless" , "Wild and thoughtless" , "Rash" , "Reckless, impetuous" .)