When one might want to change the locks? (3,4,3)
I believe the answer is:
bad hair day
'when one might want to change' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'locks?' is the wordplay.
I cannot really see how this works, but
'locks?' could be 'hair' (locks can mean hair) and 'hair' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'the' acts as a link.
Can you help me to learn more?
(Other definitions for bad hair day that I've seen before include "awful time" , "When everything makes one irritable?" , "Period when all goes wrong" , "When everything goes wrong (with one's locks?)" , "Having dodgy locks" .)