Most rum toddies will leave one drunk (6)
I believe the answer is:
oddest
'most rum' is the definition.
(I've seen this before)
'toddies will leave one drunk' is the wordplay.
'will leave' is a deletion indicator.
'one' becomes 'i' (Roman numeral).
'drunk' indicates an anagram.
'toddies' with 'i' taken away is 'toddes'.
'toddes' is an anagram of 'ODDEST'.
(Other definitions for oddest that I've seen before include "Most unusual or uneven" , "Most peculiar or strange" , "Most strange or uneven" , "Most peculiar or uneven" , "Queerest" .)