He's a failure! (3)
I believe the answer is:
Here is my best explanation:
This clue is a double definition.
'he's' is the first definition.
'a failure' is the second definition.
(dud is a kind of failure)
(Other definitions for dud that I've seen before include "Palindromic failure", "Just a palindromic flop", "Failing in its function", "Ineffectual person", "A palindromic washout", "Palindromic flop", "Non-functioning thing", "Useless, doesn't work - a palindrome", "Failed, worthless thing" and "Failing to work or meet standard (colloq.)".)