Partygoer in right state! (5)
I believe the answer is:
raver
'partygoer' is the definition.
(I've seen this before)
'right state' is the wordplay.
'right' becomes 'r' (common abbreviation).
'state' becomes 'aver' (both can mean to declare).
'r'+'aver'='RAVER'
'in' is the link.
(Other definitions for raver that I've seen before include "Wild partygoer" , "attending acid-house party?" , "one talking incoherently" , "Madman" , "Uninhibited person" .)