One coming out with lace undone — it's a fiasco (7)
I believe the answer is:
debacle
'a fiasco' is the definition.
('debacle' can be a synonym of 'fiasco')
'one coming out with lace undone' is the wordplay.
'one coming out' becomes 'deb' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'undone' indicates an anagram.
'lace' with letters rearranged gives 'acle'.
'deb'+'acle'='DEBACLE'
'it's' acts as a link.
(Other definitions for debacle that I've seen before include "Humiliating failure" , "Total disorder or defeat" , "Sudden and violent collapse" , "Sudden disastrous collapse or defeat" , "Pasting" .)