Primate's boob (6)
I believe the answer is:
howler
I believe this is a double definition.
'primate's' is the first definition.
(howler is a kind of primate)
'boob' is the second definition.
(both can mean an embarrassing mistake)
(Other definitions for howler that I've seen before include "Serious avoidable mistake" , "A glaring mistake, perhaps by schoolboy" , "Glaring mistake made by schoolboy" , "Serious blunder" , "A monkey; a bad mistake" .)