Rogue directed horse (3,3)

I believe the answer is:

bad egg

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But I can't explain it at all! Could you help me understand?

(Other definitions for bad egg that I've seen before include "Untrustworthy (a potential stinker?)" , "Not a very good person, a rotten ovum" , "A rotten ovoid" , "Rotter - something rotten!" , "Unpleasant person" .)

I've seen this clue in the Sydney Morning Herald.

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