Irritation at summit, say (5)
I believe the answer is:
'irritation' is the definition.
(I know that irritation can be written as pique)
'summit say' is the wordplay.
'summit' becomes 'peak' (mountain peak).
'say' indicates a 'sounds like' (homophone) clue.
'peak' sounds like 'PIQUE'.
'at' acts as a link.
(Other definitions for pique that I've seen before include "Arouse" , "Needle" , "Equip (anag.)" , "A feeling of hurt pride" , "Stimulate (one's curiosity)" .)