Neatnik's opposite (4)
I believe the answer is:
slob
'neatnik's opposite' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for slob that I've seen before include "Slovenly, dirty type" , "Boor" , "Sort of ice" , "Untidy and lazy person" , "Slovenly layabout" .)