One gets fed up with other people (8)
I believe the answer is:
cannibal
'with other people' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'one gets fed up' is the wordplay.
I cannot quite see how this works, but
'one' could be 'an' (an apple is one apple) and 'an' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for cannibal that I've seen before include "Eater of one's own kind" , "One who eats its own species" , "Person who eats human flesh" , "Animal that eats its own kind" , "Anthropophagite" .)