こうじつ口実koujitsu
1.
A reasoning or justification that is used to mask the true intentions or dishonesty behind an action, often crafted to seem legitimate.
2.
A rationale employed to avoid responsibility or to provide an explanation for one's behavior, typically containing deceptive elements.
3.
A phrase or statement that serves as a means to allege or accuse someone, often lacking in substance or truth.
Example:
彼女は自分に不利になるような口実を彼に与えた。