When to expect a nasty shock? (3,4,3)
I believe the answer is:
bad hair day
'when to expect' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'a nasty shock?' is the wordplay.
I cannot quite see how this works, but
'a' is within the answer.
'shock?' could be 'hair' (I've seen this before) and 'hair' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for bad hair day that I've seen before include "When everything seems to go wrong at the same time?" , "When everything makes one irritable?" , "Period when all goes wrong" , "awful time" , "When one's crowning glory is less than glorious?" .)