It's probably not good to eat nasty people with a utensil (9)
I believe the answer is:
toadstool
'it's probably not good to eat' is the definition.
(toadstools are often poisonous)
'nasty people with a utensil' is the wordplay.
'nasty people' becomes 'toads' (toad can mean an unpleasant person).
'with' says to put letters next to each other.
'a utensil' becomes 'tool' (I've seen this before).
'toads'+'tool'='TOADSTOOL'
(Other definitions for toadstool that I've seen before include "Common fungus" , "Support for little people" , "Something poisonous" , "Umbrella-shaped fungus" , "Poisonous fungus" .)