Certainly experienced expression of pain after last of unsafe cosmetic (3,6)
I believe the answer is:
eye shadow
'cosmetic' is the definition.
(I've seen this before)
'certainly experienced expression of pain after last of unsafe' is the wordplay.
'certainly' becomes 'yes' (both can be used to answer in the affirmative).
'experienced' becomes 'had' (have can mean to experience or go through).
'expression of pain' becomes 'ow'.
'after' says to put letters next to each other.
'last of' indicates one should take the final letters.
The last letter of 'unsafe' is 'e'.
'yes'+'had'+'ow'='yeshadow'
'yeshadow' put after 'e' is 'EYE-SHADOW'.
(Other definitions for eye shadow that I've seen before include "This could improve your appearance" , "Part of cosmetic treatment" , "Facial cosmetic" , "application targeted at women" , "Cosmetic for the peepers" .)