A bit vulgar to expose oneself (5)

I believe the answer is:

flash

I'm a little stuck... Click here to teach me more about this clue!

'a bit' is the definition.
(I know that flash is a type of bit)

I don't understand how the remainder of the clue works.

(Other definitions for flash that I've seen before include "Streak" , "Coruscate, second" , "beam" , "Ostentatious" , "Brandish" .)

I've seen this clue in the Sydney Morning Herald.

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