Neatnik's nightmare (4)
I believe the answer is:
slob
'neatnik's nightmare' 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 "Untidy and lazy person" , "Slovenly layabout" , "Unattractive person" , "Fat, idle type" , "Couch potato" .)