Expression of unconcern playing cameo - yes, simple thing to play (4,4,4,2)
I believe the answer is:
easy come easy go
'expression of unconcern' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'playing cameo yes simple thing to play' is the wordplay.
'playing' is an anagram indicator.
'simple' becomes 'easy' (similar in meaning).
'thing to play' becomes 'go' (I can't justify this - if you can you should give a lot more credence to this answer).
'cameo'+'yes'='cameoyes'
'cameoyes' with letters rearranged gives 'easycome'.
'easycome'+'easy'+'go'='EASY COME EASY GO'
Can you help me to learn more?
(Other definitions for easy come easy go that I've seen before include "Like a rich spendthrift's salary" , "What cost no effort to get won't be missed" , "Nineteen sixty seven film with Elvis Presley" .)