When I was 15 or so, we had two brooms: one for inside, and one for the trampoline, outside. Leaves would fall year round in Florida, as trees get confused as to whether or not it's Fall, so the trampoline broom just stayed outside because of its frequent usage. However, as I recall, this broom got so weathered that we eventually had to throw it away, leaving us with just the kitchen broom. We kept our broom beside the fridge, as per federal regulations, and would fetch it when the tramp needed sweeping.
Late one night -- let's say midnight -- I glanced through the glass doors before heading to bed, and noticed the kitchen broom had not been replaced; it was lying on the porch outside by the trampoline. In an unusual moment of fastidiousness, I opened the sliding door, went out, and closed it behind me while I went to get the broom.
(Why close it? Well, we had two cats that were not allowed outside -- ever -- and it had become an ingrained habit; you step outside, you close the door, even if it's for two seconds. We were pretty paranoid about the cats getting out and catching Typhoid.)
I grabbed the broom, and went back in the house (again opening the sliding door, going through, and closing it). It was during this second opening that Bill woke up -- he was Billy back then, age 12 or so -- and was rather frightened to hear someone coming into our home in the middle of the night.
I returned the broom to its position in the kitchen, then walked back towards my bedroom, which is just past Bill's. His door was open at night, as was mine, so we could see the nightlight in the hall. (By "nightlight" I mean "hall light" -- I don't know how we slept with a light that bright on, but apparently the dark was fearsome enough that we couldn't sleep without it.)
So I'm on my way to my bedroom, almost past Bill's door, when he jumps into his doorway in a Karate stance and yells "Hi-YA!"
That was funny. What was funnier, though, was that Bill didn't really believe somebody had come in. He was pretty sure it was his imagination, but he was going to play it safe, and use his stellar acting skills to frighten off any possible intruder. That's why, when he saw me there in the mostly-dark, he was mortified. There was a distinct moment before he recognized me as his brother that all he saw was his fears made real: there really was an intruder in the house. It was during that moment that he screamed and fell backwards.
You really need to imagine the whole scene from my perspective to truly appreciate it. Walking towards my bedroom in the still of night; my little brother jumps out in a fake Karate pose and yells "Hi-YA--", but it's cut short by his scream; his unconvincing stance disappears as he stumbles backwards in terror at seeing me. All out of the blue, all in about a second.
I wish you could have been there. (Because then we really could have scared him.)