Do something audacious: see if this thing fits (3,2,2)
I believe the answer is:
try it on
This clue is a double definition.
'do something audacious' is the first definition.
(to try it on can mean to attempt to deceive)
'see if this thing fits' is the second definition.
(Other definitions for try it on that I've seen before include "Attempt to deceive" , "test a new suit" , "See how far one may go" , "practise a little deception" , "Attempt a fitting" .)