Jokes, mostly personal, causing degradation (8)
I believe the answer is:
comedown
'degradation' is the definition.
(comedown is a kind of degradation)
'jokes mostly personal' is the wordplay.
'jokes' becomes 'comedy'.
'mostly' means to remove the last letter.
'personal' becomes 'own' (similar in meaning).
'comedy' with its last letter removed is 'comed'.
'comed'+'own'='COMEDOWN'
'causing' acts as a link.
(Other definitions for comedown that I've seen before include "Decline in status" , "Decrease" , "Descent to a lower status" , "Humiliating" , "Anticlimax" .)