That bloke with nice bum about to join conversation (5,2)
I believe the answer is:
chime in
'join conversation' is the definition.
(to chime in is to start speaking)
'that bloke with nice bum about' is the wordplay.
'that bloke with' becomes 'him' (I can't justify this - if you can you should believe this answer much more).
'bum' indicates an anagram (bum can mean faulty or wrong).
'about' indicates putting letters inside.
'nice' with letters rearranged gives 'cein'.
'him' inserted within 'cein' is 'CHIME IN'.
'to' is the link.
(Other definitions for chime in that I've seen before include "Interject a remark" , "Interrupt" .)