Crossword Genius

What spoils omelette for one poor mate? (1,3,3)

Ross

I believe the answer is:

a bad egg

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

'what spoils omelette' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'one poor mate?' is the wordplay.
I cannot really see how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is present in the answer.
'poor' could be 'bad' (similar in meaning) and 'bad' is found within the answer.
The remaining letters 'egg' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

'for' is the link.

Can you help me to learn more?

(Other definitions for a bad egg that I've seen before include "one's worthless" , "A worthless person (colloq.)" , "One undesirable customer" , "Someone inherently dishonest" , "Unpleasant guy" .)

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