It's clear to most people Apple isn't worth the money the stock markets assign it - well over half their cap is investment in the brand.
If they ever do anything to damage that or if they do something even remotely wrong, a whole lot of people are going to lose a whole lot of money.
I said it depends on Apple doing something wrong and I can't predict when that'll happen or what it'll be but here are some suggestions: Making the iPhone 7 out of cheese or Tim Cook farting in the wrong direction. Either way, if the markets have shown us anything in the past, it doesn't take much at the moment to send traders into sellmageddon mode.
It costs money to keep short positions open - there are several examples of people who exited short positions in the subprime-mortgage bond market just before the credit crunch. They were convinced that the market was going to crash, but they didn't know exactly when.