Flippant, for instance, about a piece of luck (5)
I believe the answer is:
saucy
'flippant' is the definition.
(I've seen this in another clue)
'for instance about a piece of luck' is the wordplay.
'for instance' becomes 'say' (both can be used to introduce an example).
'about' is an insertion indicator.
'a piece of luck' becomes 'uc' (I can't explain this - if you can you should give a lot more credence to this answer).
'say' enclosing 'uc' is 'SAUCY'.
Can you help me to learn more?
(Other definitions for saucy that I've seen before include "Cheeky, impertinent" , "Impertinent - jaunty" , "Risque" , "Pert and toothsome" , "Cheeky; risquZ" .)