Cheerfully reckless (5-3-4)
I believe the answer is:
devil-may-care
'cheerfully reckless' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for devil-may-care that I've seen before include "Negligent" , "Cheerful, reckless" , "Reckless, audacious" , "Insouciant (attitude)" , "Reckless - mediaeval cry (anag)" .)