Hard to miss that lady's right boob (3)
I believe the answer is:
err
'boob' is the definition.
(both can mean to make an error)
'hard to miss that lady's right' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'to miss' is a deletion indicator.
'that lady's' becomes 'her' (belonging to a lady).
'right' becomes 'r' (common abbreviation).
'her' with 'h' taken away is 'er'.
'er'+'r'='ERR'
(Other definitions for err that I've seen before include "Blunder" , "Make mistakes" , "Be incorrect" , "Go astray" , "Slip up" .)