My senior year prank was on the drum line (I was lead snare, and the only senior), where I took the top drumhead off of the snares and took one of the 5th base drum's heads off, and put pinups inside of them, before putting the heads back. They haven't replaced heads yet, and because of the type of drum heads we use you can't see through the bottom head at all. I'm still waiting for that bomb to be discovered.
Another one that's worse.
Whilst smoking a cigarette at the ripe age of 15, my cat scared the utter shit out of me and the butt flew into the trashcan. I figured it was out because the cherry fell on the floor near the trashcan, so I doused the cherry and cleaned that up and went outside to go hang with some friends. I came back to the kitchen filled with smoke, as well as the main floor of my house being cloudy due to the trashcan being on fire. With no fire extinguisher handy (it was behind the fucking trashcan) I picked the flaming plastic up and threw it in my yard where I doused it with a hose. I guess nobody saw, or told my parents, and I got away without my parents figuring out I almost burned the house down. The trashcan was fine too, somehow. I mean sure it had a huge brown spot from melted plastic inside of it, but since I was the only one that dealt with taking the trash out, it wasn't a big deal. The odd part, was the only reason I came home was I had this really, really bad feeling. Any time I get that feeling now, I know I need to do the first thing that pops to mind afterwards. It's kept my girlfriend from cutting herself, my mom from committing suicide, and my friend from getting run over by a car (though his bike did not fare as well).
And another from my school years about cheating.
I once "cheated" on a chemistry test. I was going to use this one, but my entire chem class knows about it, so it isn't really one or two people. We basically had to memorize a list of 50 ionic compounds, their charges, and chemical makeup. We were given a total of 48 hours to do this, because, y'know, I was in a freaking AP class so we were supposed to be awesome or something (funny thing is, all of us failed the AP test because the teacher didn't teach 1/2 of the content on it. Sounds like an excuse, but I am serious. All he had to say was sorry. I digress though.) and basically everyone decided they were going to cheat. I made a list of the compounds, charges, and makeup on a folded up half sheet of paper 3 hours before the test. I then transcribed that onto 1/4 of a sheet, and so on and so forth until I had around 6 sheets that were all around 6cm long and 4cm wide. During lunch before the class, I realized that I had spent so long writing those damn things out, making sure the words were legible and matched properly (think size 1 font, I was sharpening my pencil every word) that I knew all of the compounds, charges, and chemical formulas. I handed out those cheat sheets and didn't use one. I think I was the only person to that legitimately received a 100%.
On my statistics final in math my senior year, 5 minutes before the test began a mass text was sent to everyone in the classroom that contained the test answers. Too bad there were 2 versions of the test. I noticed this, and tipped off two of my very close friends, who had also noticed and were trying to tip me off. I wasn't actually going to use it to cheat, and I doubt my friends would have, but I did happen to glance at the answers and notice that there were 2 versions of the test. I proceeded to finish my test as normal and turn it in when I was done, and talked to the teacher for a bit. I was one of the last people to turn it in, because 10 minutes into the class almost everyone got up and turned their tests in that they had blindly copied. As I walked back to my seat, I proclaimed in a loudish voice (and I still remember this perfectly, it will forever be cemented) that "I'm sure glad that the 3rd question on my test wasn't the same as Kevin's." which left the room in silence (my class were being assholes and talking because they *finished* early). Que everyone getting up attempting to get their test back, the teacher finding out almost everyone was cheating, multiple people failing, and a redo of the test for everyone suspected of cheating, but a lack of proof being had to confirm it. I think out of my class of 48, 18 failed immediately due to cheating, 7 failed the final because they didn't know the material when they redid the test, and either 6 or 7 of us for sure didn't cheat (we had the version that was not mass texted and didn't copy answers from the wrong version onto ours (seriously who would do that? really?)). Everyone else redid the test and passed with varying results. I feel slightly responsible for my class size dwindling ever more slightly than it already had.