For those wishing for immortality...
Immortality (from Cracked.com)
Okay, after the first, say, few hundred years, everything's still fine and well. You've seen a few generations of people live and die, and had this happen to your family. Oh well, they were likely douches you could live without anyway at some points. Companionship is companionship, or so you think.
Not so fast: You know how when you were younger (by human terms, a child), an hour seemed like forever to you? As people grow, their brain starts to perceive time differently. An hour feels like less time. Now extend that logic to a year, or a decade, or a century. This means that eventually, you will be completely unable to form relationships with human beings because their lives and deaths will flash past you like a tape on fast-forward. [Even if you don't buy that it gets worse...]
Let's keep going into the future, since you're a sociopathic recluse and think you're still okay with this whole immortality thing. There are so many things that could go wrong with the planet, an asteroid strike, nuclear war, the LHC, but let's assume the planet somehow makes it through all that without being reduced to dust.
Five billion years from now or so, the Sun expands into a red giant. You survive the first roasting, but nothing else does. The Sun eventually rips planet Earth into rubble with gravity. So now there you are floating in outer space, drifting along, or getting a bitching tan at the heart of the Sun so you can pick up some killer alien chicks in the Andromeda galaxy if you ever get there (you won't).
Either way, a few trillion years later, the universe starts to really show its entropy. Every where is the same. No stars, no planets, no black holes, just an empty, cold mass of subatomic particles that can never come together again. And you, floating along in the void. Forever.