Messy one (4)
I believe the answer is:
slob
'messy one' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for slob that I've seen before include "'Slovenly, messy person (4)'" , "Unattractive person" , "Boor" , "Sort of ice" , "Slovenly and unkempt type" .)