A mistake, whichever way you look at it (4)
I believe the answer is:
boob
This clue is a double definition.
'a mistake' is the first definition.
(I've seen this before)
'whichever way you look at it' is the second definition.
(Other definitions for boob that I've seen before include "Error" , "Blunder (colloq.)" , "Mistake; breast (sl.)" , "Embarrassing mistake" , "Slip" .)