A friend once told me that his vision of Hell was being forced to watch, over and over again for all eternity, movies of every incident in in your life in which you hurt someone (although I suppose this is only effective if you are not afflicted with antisocial personality disorder).
Running out of maple syrup before I finish my waffles.
Having to substitute pancake syrup for real maple syrup.
For me, the realization that there is a lot (too much) sadism in the world. This realization came when I started volunteering in international dog rescue. As bad as neglect is, outright sadism is unforgivable. I’ve heard of too many animals rescued from scenarios where you can just visualize the perpetrators standing around drinking beer and laughing at the screams. (I also need brain bleach.)
It only got worse with all the torture news coming out of the middle east and I realized that we’ll never “solve” animal cruelty in the world until we “solve” human cruelty. And that’s not happening any time soon. 
For a lighter answer: How about the square of i (imaginary number)?
Not only is it negative, but also not real and not cool. No wonder its absolute value is the loneliest number.
Of course not, I’m an atheist. But the OP didn’t ask for what I* believed;* it asked for what I could imagine.
Limp bacon.
A never-ending toothache, for the rest of my life, with no remedy in sight. I’d rather have a migraine.
I ain’t got no none unnegatives never nohow.
Well, I tried posting:
[noparse] -∞ [/noparse]
but when I tried to preview it, my browser imploded trying to display it and reduced my computer to a singularity. (ETA: Yes, I’m posting from my neighbor’s computer now.)
Ooooooooo, I wanna see!
Ninjaed!