The car was filthy when he returned it to me, and 'to cap it off' [='to top it off'], there was almost no fuel left in the tank.
a 'shower/bathing cap' [=a head covering that people wear to keep their hair dry when they are showering/swimming]
They may not like being called careless, but 'if the cap fits, wear it'. [=('US') 'if the shoe fits, wear it']
(..) - No! It looks good. No. Look... leather jacket, without sleeves, stud bracelets. A Village People-like cap. I know! Jos' Bov'. You look exactly like him. Really weird. An orthodox priest or something. - The pope. (..)2011 Intouchables