Misses one most, being crazy about (5)
I believe the answer is:
omits
'misses' is the definition.
('omit' can be a synonym of 'miss')
'one most being crazy about' is the wordplay.
'one' becomes 'i' (Roman numeral).
'being crazy' indicates an anagram.
'about' means one lot of letters goes inside another.
'most' anagrammed gives 'omts'.
'i' going into 'omts' is 'OMITS'.
(Other definitions for omits that I've seen before include "misses out" , "Leaves out or neglects" , "skips" , "Forgets" , "overlooks" .)