It’s mischievous and egotistic to go topless (6)
I believe the answer is:
elfish
'it's mischievous' is the definition.
(synonyms)
'egotistic to go topless' is the wordplay.
'egotistic' becomes 'selfish' (similar in meaning).
'to go topless' means to remove the first letter.
'selfish' with its first letter taken away is 'ELFISH'.
'and' acts as a link.
(Other definitions for elfish that I've seen before include "Mischievous" , "Tricky" .)