I sometimes have thoughts of suicide. That does not mean I would ever come within a mile of committing the act of suicide. But my brain does simulate it; though I do try to always reduce such thoughts.

But what I have noticed is that 'suicide' is triggered in my mind whenever I think of some embarrassing event, real or imagined. Or an event in which I'm obviously a low-status actor. This leads me to think that suicide might be a high-status move, in the sense that its goal is to recover status after some event which caused a big drop in status. Consider the following instances when suicide is often considered:

1. One-sided break-ups of romantic relationships. The party who has been 'dumped' (for the lack of a better word), has obviously taken a giant status hit. In this case, suicide is often threatened. 
2. A samurai committing seppuku. The samurai has lost in battle. Clearly, a huge drop in status (aka 'honor').
3. PhD student says he/she can't take it anymore. A PhD is a constant hit in status: you aren't smart enough, you don't have much money, and you don't yet have intellectual status.