He possibly is angriest when drunk (5,3)
I believe the answer is:
inert gas
'he possibly' is the definition.
(helium - symbol 'He' - is an example)
'angriest when drunk' is the wordplay.
'when drunk' indicates an anagram (a drunken or disorderly form of the letters).
'angriest' is an anagram of 'INERT GAS'.
'is' is the link.
(Other definitions for inert gas that I've seen before include "one at the edge of a table" , "Unreactive "noble" element, such as argon" , "One expects no reaction from such" , "Passive element in the helium group" , "He perhaps" .)