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']
(..) But... since that's what it looked like, we can rule that out. Let's put on our thinking cap, shall we? Raj is from India, a tropical country. Third World hygiene. Parasitic infections are common, such as pinworms. (..)2011 TvShow: The Big Bang Theory Title: The Skank Reflex Analysis Season: 5 Episode 1