It's been a while since I did these things, but they still make me laugh.
Stupid Kid Thing #1
Push M80-M100 firecrackers into manhole covers (there's usually a little hole for them to insert the pick). Then run like hell and watch the cover pop up out of the road with a big bang.
Stupid Kid Thing #2
Me and my above friend had a sort of thing for anything that exploded or flew. So, we naturally had some bottlerockets. Our neighborhood was filled with kids that were about 5 years younger than us, so we had plenty to pick on. We proceeded to go underneath my house (more of a crawl space than a basement) and cut out a little space on the vent to allow a bottle rocket to shoot out. We then proceeded to shoot bottlerockets at the little kids riding their bikes and tricycles across the street. My neighbor came running over to see what was going on, and we just pretended that we were just watching TV and had no idea what those big bangs were. She never did figure it out. That basement "launch pad" was a perfect spot.
Stupid Kid Thing #3
I went to a Catholic school and one of my friends worked in the main office. When nobody was looking, he figured out the code to modify the answering machine messages from another phone. We would routinely, at least once a week, leave a "appropriate" message on the machine. This went on for weeks before they finally wised up and locked up the stupid answering machine.
'00 2.5RS Sedan
'72 Datsun 240Z