A few ways you can play this, not necessarily being the lower rank you do not have your ways:
Choice 1: Find out which other officer/ senior NCO in the unit has a beef with him. Send this guy an anoynomous letter about the situation and let loose the rumors against him. Sooner or later the following may happen - (A) his commanding officer hear about it and tell him to be more aware and he just lan lan have to let things go, (B) some senior staff with a grudge or personal agenda will forward this to somewhere and blow it up to get rid of him or (C) he is aware that everyone knows and decides to stop due to the peer pressure.
Choice 2: Get one guy and go to S1 (or the S1 clerk) and say he is thinking of committing sucide. This will set off the alarm bells and everyone will start to take it seriously. But must really know how to act. Get the guy who always ganna tekan by this officer.
This is just 2 ways. I have more. Must learn to play the "GAME' mah. SAF is not owned by him, it is a big and complex system. If you know the system well, you CAN fight back.