Philosopher irritated when declared to be like everyone else (8)
I believe the answer is:
humanoid
'like everyone else' is the definition.
(like a human)
'philosopher irritated when declared to be' is the wordplay.
I cannot really understand how this works, but
'be' could be 'hum' (humming is a kind of being) and 'hum' is found within the answer.
This explanation may well be incorrect...
(Other definitions for humanoid that I've seen before include "Creature resembling man" , "Like a person" .)