That's a non-starter.

Meaning

That's an unacceptable idea or proposal.

Examples

• John: I think we should postpone the launch until next quarter.
• Alice: <b>That's a non-starter</b>. The deadline is fixed.
• John: But we're facing significant delays.
• Alice: I understand, but postponing is not an option. <b>That's a non-starter</b>.