Jūnrén shànlízhíshǒu shì yánzhòng de wéijì xíngwéi.
For a soldier, going AWOL is a serious breach of discipline.
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Formal and often legalistic, common in HR policies, military regulations, and court judgements. The daily conversational equivalent would be 擅自离岗 or simply 没打招呼就走了.