His being so close upsets me sir (5)
I believe the answer is:
miser
'his being so close' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'upsets me sir' is the wordplay.
'upsets' indicates an anagram.
'me'+'sir'='mesir'
'mesir' anagrammed gives 'MISER'.
Can you help me to learn more?
(Other definitions for miser that I've seen before include "One's tight" , "One such as Scrooge" , "One doesn't spend much" , "Cheeseparing person" , "Hoarder of money and possessions" .)