Put a mock warning out? I am surprised at you! (3,5)

I believe the answer is:

for shame

I'm a little stuck... Click here to teach me more about this clue!

'out? i am surprised at you' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'put a mock warning' is the wordplay.
'put' means one lot of letters goes inside another.
'a mock' becomes 'sham' (I've seen this in another clue).
'warning' becomes 'fore' (shouted in golf).
'sham' going inside 'fore' is 'FOR SHAME'.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app