horror story ideas?

Any ideas? I have to write one for school and I'm blank. I'm looking for something more freaky than scary, if you know what I mean- the kind of story where the main character doesn't find out they're dead until the last sentence, or turns out to be the villain. Something with a really twisted, unexpected ending.

Any ideas are welcome!

This is a gem I've been hoarding for years, but I've yet to tackle the challenge of turning it into a story, so I'll bequeath it to you. Treat it gently.

During the tail-end of winter a boy buys a short-sleeved T-shirt at a thrift shop. He loves the shirt -- perhaps it has his favourite team logo on it, or something of that nature; be creative -- and wears it everywhere, reveling as he does so in the warm weather. One morning he gets up, puts on the shirt, and finds its sleeves are a tad longer. Strange, he thinks, but maybe his mind is playing tricks on him. The next morning the sleeves are even longer. That's impossible, he thinks, but school has him too busy to worry. Gradually, insidiously, the sleeves grow longer still; and though he doesn't understand how, neither does he tell a soul: surely they'd think him crazy. Finally the shirt stops growing, the cuffs of the sleeves coming neatly to the ends of his wrists.

One overcast day in June, the temperature in the high sixties, he decides to wear the shirt again, figuring it's cool enough for long sleeves, so why not? Around noon he plays a pick-up game of basketball on the school court and dies of heatstroke.

Brilliant, thank you!

Prokaryote, I would like to mention that your signature is relevant to that comment (although I don't know what it's from). Also, thank you for your username reminding me to stop procrastinating via YWS, and get back to my science homework involving cells-kinda-sorta. Which I should probably do... now.