13 across
Damning
evidence
of
bad
habit:
one’s
shot
(7,3)
Damning evidence of bad habit: one’s shot (7,3)
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The definition is at the beginning of the clue.
How the clue works
The definition is Damning evidence, which is what a smoking gun is in the figurative sense. The wordplay is a charade of SMOKING (the bad habit) followed by GUN (the thing that fires a shot).