This happened at my friend's house a couple years ago. It was the first time she'd thrown a big party like this for Halloween.
A couple of my friends and I ended up spending the night there, because no one was in any shape or mood to drive home at two in the morning.
We crashed in her living room. The house was small, and it only had one floor. The living room is to the right of the front door, lots of windows, and a big pond out in the front.
Everything else is an empty field. Adjacent to the living room was the dining room and the kitchen. To the left of it, you've got your classic creepy hallway, complete with an old dusty mirror at the end of it.
There were about seven of us total, sitting in the living room, when all of a sudden, my friend stopped, claiming she heard a noise. So, she and another one of the guests went down the hall to have a look as the rest of us continued to doze off. That was, until they came running out, shutting the curtains and turning off as many lights as they could. They urged us to do the same. We shut all the curtains and turned off every light in the house save for a couple of flashlights. That's when our lovely hostess started handing out steak and butcher knives for "protection."
At this point, the rest of us just wanted to understand just what the fuck got them so upset. Apparently, they'd gotten halfway down the hallway when one of them noticed a movement in the corner of her eye. She looked into the office, the first door on the right which faced the front of the house. There was a handprint on the window.
This would only seem a little odd. But the handprint was on the outside of the window, and had never been there before. Mind you this was a small house. We were partying all over the place. Someone had to have been outside in the last ten or twenty minutes to make it. The only other problem was that the window in question was elevated two metres off from the floor. As far as I'm concerned, no one at the party was two and a half metres tall.
By now, all of us were thoroughly freaked out about the fresh handprint. Except for me. Me, being oddly disinterested in freaky shit, went outside to see the handprint. That's when I realised how tall you actually had to be to make a handprint at the top of the window like that. I figured no one else had noticed yet. Besides, scaring people who are holding steak knives is a stupid idea.
I went back in to check on everyone. They'd considered calling the cops, but the house wasn't made with a working land-line, causing the reception to go to shit. I decided to calm everyone down and tried to convince them that some guy got proper plastered and just hopped up to slap the window like that. Since no one had considered the height of the window, they believed me all the way to the next morning.
When everyone went to sleep at night, I didn't. I ended up staying up, because I knew the one thing that I hadn't told everybody.
I knew the truth, and I figured I should be awake in case there was a break-in. I had to use the bathroom earlier that night, and I found a similar hand-print on the bathroom window, which happened to be at least half a metre higher than the one the others had found. And when I walked outside, I realized that half the windows on the front of the house had handprints. But to this day...I think I'm the only one who has discovered that.