Horror stories to give you nightmares

The man

One night while babysitting my neighbors children, I saw a man through the window of the living room while I was watching tv.
At first, I just ignored it, but then the man showed up again after a few minutes. I tried ignoring it again, assuming it was just my imagination going crazy.
Then, I saw him again, but this time he was much closer. So I called the parents and told them that there was a man outside of the window, and they replied with, "we don't have any Windows in the house, only mirrors."