He gets fed up with people (8)
I believe the answer is:
cannibal
'he gets fed up with people' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he' is the wordplay.
I cannot really see how this works, but
'he' could be 'al' and 'al' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for cannibal that I've seen before include "Person who has someone for dinner?" , "One with odd eating habits" , "One eats human flesh" , "Person who eats human flesh" , "Animal that eats it own kid (8)." .)