Argue about distribution of loot? He'll side with the boss (10)
I believe the answer is:
bootlicker
'he'll side with the boss' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'argue about distribution of loot?' is the wordplay.
'argue' becomes 'bicker' (bickering is a kind of arguing).
'about' indicates putting letters inside.
'distribution of' indicates anagramming the letters.
'loot' is an anagram of 'ootl'.
'bicker' placed around 'ootl' is 'BOOTLICKER'.
Can you help me to learn more?
(Other definitions for bootlicker that I've seen before include "Sycophant" , "Toady" , "who may ensure that tongues meet" , "Ingratiating type" .)