Mischievous libertine pinching prig's backside (5)
I believe the answer is:
rogue
'mischievous libertine pinching prig's backside' is the definition.
I can't judge whether this definition defines the answer.
'libertine pinching prig's backside' is the wordplay.
'libertine' becomes 'roue' (roue is a kind of libertine).
'pinching' means one lot of letters goes inside another (taking inside).
'backside' suggests the final letters (the letter at the back).
The final letter of 'prig' is 'g'.
'roue' going around 'g' is 'ROGUE'.
Can you help me to learn more?
(Other definitions for rogue that I've seen before include "Villain - freak" , "One dishonest" , "Bad guy" , "Blackguard" , "Dishonest man" .)