Eager to see thin, sauciest pants (12)
I believe the answer is:
enthusiastic
'eager' is the definition.
('enthusiastic' can be similar in meaning to 'eager')
'thin sauciest pants' is the wordplay.
'pants' indicates anagramming the letters (UK informal term for 'nonsense' or 'rubbish').
'thin'+'sauciest'='thinsauciest'
'thinsauciest' with letters rearranged gives 'ENTHUSIASTIC'.
'to see' acts as a link.
(Other definitions for enthusiastic that I've seen before include "hot" , "Intensely keen and interested" , "Gung-ho" , "Ardent - thin suitcase (anag)" , "Full of fervour" .)