Somewhat curiously, throughout film history there's a surprisingly virile thread of bungled suicide as comedy, whether it's played for outright laughs, as in Bachelor Party and The Man In The Iron Mask (with added grotesque male nudity,) or for touching pathos, as in The Full Monty and Little Miss Sunshine. Apparently the utter despair of central characters is appropriate content to inspire a few disposable chuckles. But what about the tragic examples when characters are driven to suicide, and find themselves impotently unable to carry out their singular, morbid intention. They aren't convinced to change their minds, per se, (not in the majority of cases, anyway) or overcome by the necessary moral arc of their narrative (as in the case of Travis Bickle,) instead they are the grim personification of Tantalus, compelled by desire, but restrained by tragic circumstance. In the immortal words of the almost immortal T-1000 at the climax of Terminator 2, this tragic band of characters cannot "self-terminate," regardless of how much they want to. They are the damned, doomed to live half lives, and unable to bring it all to an end thanks to circumstances, logistics or the unhelpful, unrequested assistance of Good Samaritans.
Honourable Mention
Hancock Though it never ended up on screens, the original version of post-superhero comedy of two halves Hancock was far darker than the horribly sanitised final version we got to see that took a wonderfully engaging concept and pushed it through a pulveriser until very little worked by the end. As part of the original ending, Hancock can't get over his obsession with Mary (Charlize Theron,) who wasn't intended to be his super-beloved originally - and just a random hottie he encounters, kidnaps and plans to rape. Cheerful. The darker tone would have been much better, but the studios clearly thought Will Smith and rape didn't go together so well, and the second half of the film was toned down, including the removal of Hancock's attempted suicide scene, when he is overcome by self-loathing and decides to end it all, only to discover that his immortality also covers suicide attempts.