The recent thread about "supernatural" experiences helped me to remember the times I enjoyed playing frightening pranks on people.
Example #1: Years ago the employees at a place I worked for had a 40th birthday party for one of the women we worked with. It was a typical "somber and dark" humorous party with black balloons, black candles on the birthday cake... all meant to suggest that at 40 ife as you know it is just about over. It's funny, but 25 years after my 40th birthday I'm yearning for those days when things were better.
...but I digress. The party was good-natures fun and everyone had a nice time. After the party during the clean-up, somehoe some inflated black balloons found their way into a large storage closet - a large walk-in windowless closet with racks for storage of printed literature, equipment that might find use in a meeting (projectors, TVs, VCRs, etc.). Time passed, and the black balloon deflated a bit and began to collect a nice film of dust on its surface which was held in place by static electricity. This completely changed the way the ballon looked... it didn't resemble a balloon anymore, it looked like a cannon-ball, which is what I first thought it was when I saw it patiently sitting there.
I picked the "cannon-ball" up with both hands and held it in front of myself with my shoulders rounded as they might be had this really been a 50-pound (24 kilo) cannon ball. I shuffled up to the desk where one of the guys I worked with was sitting and said, "Why do we have a cannon-ball in the storage closet?" as I tossed the "cannon-ball" toward him in an arc that would have had it land in his lap had it really been a 50-pound ball of iron.
BOY did he jump to protect the family jewels!
I've got a couple other examples I can share, but they'll each take a bit of time to type up, so I'll add them later if there is any interest.