Petition against becoming judge - it's funny to some (2-4)
I believe the answer is:
in-joke
'petition against becoming judge' is the definition.
I know nothing about this answer so I can't judge whether this works.
'funny to some' is the wordplay.
'funny' becomes 'joke' (I've seen this before).
'to' means one lot of letters go next to another (I've seen this in other clues).
'some' becomes 'in' (I can't justify this - if you can you should believe this answer much more).
'joke' put after 'in' is 'IN-JOKE'.
'it's' acts as a link.
(Other definitions for in-joke that I've seen before include "Exclusive gag?" , "Humour understood by a small group" , "Humour exclusive to a small group" , "Gag understood only by a small group" .)