Joker initially pretty disgusting - rest wandered off (9)
I believe the answer is:
prankster
'joker' is the definition.
(I've seen this before)
'initially pretty disgusting rest wandered off' is the wordplay.
'initially' indicates taking the first letters.
'disgusting' becomes 'rank'.
'wandered off' is an anagram indicator (I've seen 'wandering off' mean this (I've seen this in other clues)).
The initial letter of 'pretty' is 'p'.
'rest' with letters rearranged gives 'ster'.
'p'+'rank'+'ster'='PRANKSTER'
(Other definitions for prankster that I've seen before include "Practical joker" , "Wag" .)