Irritable desire to eat snake (7)
I believe the answer is:
waspish
'irritable' is the definition.
(thesaurus)
'desire to eat snake' is the wordplay.
'desire' becomes 'wish' (wishing is a kind of desiring).
'to eat' is an insertion indicator.
'snake' becomes 'asp' (asp is a kind of snake).
'wish' placed around 'asp' is 'WASPISH'.
(Other definitions for waspish that I've seen before include "Bad-tempered like striped insect" , "Bad-tempered like striped stinger" , "Sharply irritable" , "irascible" , "'Very irritable, like a stinger (7)'" .)