Both shout wickedly about rookie's first sort of moustache (10)
I believe the answer is:
toothbrush
'sort of moustache' is the definition.
(I know that toothbrush is a type of moustache)
'both shout wickedly about rookie's first' is the wordplay.
'wickedly' indicates an anagram.
'about' is an insertion indicator.
'rookie's first' becomes 'r' (1st letter of 'rookie').
'both'+'shout'='bothshout'
'bothshout' with letters rearranged gives 'toothbush'.
'toothbush' enclosing 'r' is 'TOOTHBRUSH'.
(Other definitions for toothbrush that I've seen before include "One found in toilet bag" , "Dental cleaner" .)