The old man's entertaining celebrity baddies (8)
I believe the answer is:
dastards
'baddies' is the definition.
'the old man's entertaining celebrity' is the wordplay.
'the old man's' becomes 'dads' ('dad' can be a synonym of 'old man').
'entertaining' is an insertion indicator.
'celebrity' becomes 'star' (I've seen this before).
'dads' going around 'star' is 'DASTARDS'.
(Other definitions for dastards that I've seen before include "scoundrels" , "Cowards" .)