Amuses Mark and Leslie! (7)
I believe the answer is:
tickles
'amuses' is the definition.
(I've seen this before)
'mark and leslie' is the wordplay.
'mark' becomes 'tick' (I've seen this before).
'and' is a charade indicator (letters next to each other).
'leslie' becomes 'les' (short for Leslie).
'tick'+'les'='TICKLES'
(Other definitions for tickles that I've seen before include "Light touches that cause laughter" , "Excites" , "Soft touches" , "Amuses" .)