Bully, perhaps, volunteers what everyone passes (7)
I believe the answer is:
taurine
'bully perhaps' is the definition.
(taurine means like a bull)
'volunteers what everyone passes' is the wordplay.
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'what everyone passes' becomes 'urine' (everybody passes urine).
'ta'+'urine'='TAURINE'
(Other definitions for taurine that I've seen before include "Bullish" , "Resembling a bull" , "Nature I associate with bull-like quality" , "organic compound" , "Ruinate, being like bull" .)