They're picked by the picky (4)
I believe the answer is:
nits
'they're picked by the picky' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for nits that I've seen before include "Tins of parasitic insect eggs" , "Eggs; stupid people" , "Eggs of lice" , "Head lice" , "Fools" .)