I chased a friend of mine with a Swiss Army knife
In my defence, he wouldn't shut up about the Dark Knight, so I screamed WHY SO SERIOUS and chased him for half an hour. To doubly scare him, whenever he'd loose sight of me I'd stop running and start shambling with the knife held over my head like a demented, armed zombie.
That same friend, however, has done some crazy shizz WITH me as well
On a few occasions, we chased the rabbits in the fields near my house. I was talking about how my dog chases them and he seems to have a great time, so me and this other friend, wordlessly and simaltaneously, abandoned the rest of our group and pelted down the hill after the damn rabbits
Also, in the same fields, we were both walking directly behind the rest of the 'gang'. We looked at each other and, without even discussing it, both collapsed on the floor. It was nighttime and we wore dark clothes, so we were invisible. Our friends turn around, their feet LITERALLY next to our noses, and they couldn't see us and thought we'd run away. We then stalked them the entire way home, freaking them out before jumping out at them.
I did a similar thing in Peru, when all the guys were sneaking about letting down the girls' tents with them in them. I told that story about the hiding and they didn't believe me. I went away, got changed into my black silk thermal underwear (longjohns/ninja outfit), my black silk glove linings and borrowed a balaclava from John. I looked like a ninja. When we let down the girls' tent again, Hugh and Will ran away, but I lay down like I did with my other friend. Laura came out, angrily, and was laughing privately with the other girls over how Will and Hugh (both in white sport shirts) thought they were invisible behind the bush about four hundred feet away. She craned her neck to find me (remember, I'm mere inches away from kissing her boots) "Where's Ali?"
"Down here"
She screamed SO loud
