Bunk's ladder broken during party (10)
I believe the answer is:
balderdash
'bunk's' is the definition.
(I've seen this before)
'ladder broken during party' is the wordplay.
'broken' indicates an anagram.
'during' is an insertion indicator.
'party' becomes 'bash' (term for a party or celebration).
'ladder' with letters rearranged gives 'lderda'.
'lderda' placed inside 'bash' is 'BALDERDASH'.
(Other definitions for balderdash that I've seen before include "Piffle" , "Rubbish" , "stupid talk" , "Bunk" , "bull" .)