Pal has no right to be such a nasty person (5)
I believe the answer is:
fiend
'such a nasty person' is the definition.
(a fiend is a bad person)
'pal has no right' is the wordplay.
'pal' becomes 'friend' (I've seen this before).
'has no' suggests deleting specific letters.
'right' becomes 'r' (common abbreviation).
'friend' with 'r' removed is 'FIEND'.
'to be' is the link.
(Other definitions for fiend that I've seen before include "Evil supernatural being" , "Operatic super-soprano" , "Devil" , "Wicked and inhuman person" , "Demon, ogre" .)