You could find a story around that. A bad breakup with a cheating girlfriend, or a dead end job.
Check this out:
The guy finds himself in his apartment, alone.
The first thing we see is him setting up the camera on a tripod. «It would be great to film this on a cheap camera. The one on the tripod, just lik if you wher making a suicide tape»
He takes a seat, he has a paper on his hand.
"The test came back positive" is what we hear him mutter, and he starts ranting about his cheating girlfriend and hated job, breaking the news of his soon to be suicide to the viewer.
Add a monologue here telling something of his day to day life. Make his phone ring. Apperently is a co-worker, worried about him not coming in that day. He answers that everythingis okay, that he is "not feeling well".
In the end, he goes to another room, of which the door is seen. We see a big flash and hear a gun going off.
Just seconds go by, for his answer machine to pick up a call.
"This is Joan from doctor Behinaker's office. Your test results are negative Mr.Character. Somehow samples got mixed up at the lab. If you want, we can schedule a free of charge [start fade to black] test for you to be sure. Sorry for the inconvience. [Fade to black]