Disparaging outsider's first to take part in unfortunate jeer at VIP (10)
I believe the answer is:
pejorative
'disparaging' is the definition.
(thesaurus)
'outsider's first to take part in unfortunate jeer at vip' is the wordplay.
'first' suggests taking the first letters.
'to take part in' is an insertion indicator.
'unfortunate' indicates an anagram.
The initial letter of 'outsiders' is 'o'.
'jeer'+'at'+'vip'='jeeratvip'
'jeeratvip' with letters rearranged gives 'pejrative'.
'o' inserted within 'pejrative' is 'PEJORATIVE'.
(Other definitions for pejorative that I've seen before include "Disparaging" , "putting down" , "Unpleasant" , "Expressing contempt or disapproval" .)