About to regret getting note that’s vulgar (5)
I believe the answer is:
crude
'vulgar' is the definition.
(I know that vulgar can be written as crude)
'about to regret getting note' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'to regret' becomes 'rue' (to rue something is to regret it).
'getting' is an insertion indicator.
'note' becomes 'd' (musical note).
'rue' placed around 'd' is 'rude'.
'c'+'rude'='CRUDE'
'that's' is the link.
(Other definitions for crude that I've seen before include "Rough or undeveloped" , "foul-mouthed?" , "Oil; rough" , "Rude; raw" , "Cured (anag.)" .)