Wobbling shapely bum? Heartless and an unacceptable thing to say (9)

I believe the answer is:

blasphemy

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

'an unacceptable thing to say' is the definition.
I can't tell whether this definition defines the answer.

'wobbling shapely bum? heartless' is the wordplay.
'wobbling' indicates an anagram.
'heartless' says to hollow out the word (remove centre letters).
'bum' with its centre removed is 'bm'.
'shapely'+'bm'='shapelybm'
'shapelybm' anagrammed gives 'BLASPHEMY'.

'and' is the link.

Can you help me to learn more?

(Other definitions for blasphemy that I've seen before include "swearing" , "Sacrilege, profane speech" , "Profane talk or behaviour" , "Profane words" , "Sacrilegious talk" .)

I've seen this clue in The Guardian.

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