Distressed diner with gun, standing (8)
I believe the answer is:
enduring
'standing' is the definition.
('endure' can be a synonym of 'stand')
'distressed diner with gun' is the wordplay.
'distressed' is an anagram indicator.
'with' is a charade indicator (letters next to each other).
'diner' after 'gun' is 'gundiner'.
'gundiner' with letters rearranged gives 'ENDURING'.
(Other definitions for enduring that I've seen before include "stable ..." , "Putting up with patiently" , "Permanent" , "Bearing patiently or lasting" , "Lasting a very long time, despite hardship (8)" .)