Eagerness to get at mince pie's deplorable (10)
I believe the answer is:
'eagerness' is the definition.
'at mince pie's deplorable' is the wordplay.
'deplorable' indicates anagramming the letters.
'atmincepie' anagrammed gives 'IMPATIENCE'.
'to get' acts as a link.
(Other definitions for impatience that I've seen before include "Irritation at delay" , "Unreasonable haste" , "Lack of tolerance" , "which poor waiter reveals" , "agitation" .)