A savage who gets fed up with other people (8)
I believe the answer is:
cannibal
'a savage' is the definition.
(cannibal is a kind of savage)
I don't understand the rest of the clue.
(Other definitions for cannibal that I've seen before include "Animal that eats it own kid (8)." , "Animal that eats its own kind" , "Eater of one's own kind" , "One with odd eating habits" , "Person who eats human flesh" .)