A couple we did as Seniors throughout the last month of school.
Walked into an often used restroom in between 4th and 5th hour, lit an M-80, counted to 2, flushed it and briskly walked out. Turns out a Freshman was in the last stall dropping a deuce....Whoops. The urinal I flushed it in, removed itself from the wall and the pipe showered water for about 10 minutes.
My buddy had 3 lab puppies and one was a "quiet one". We labeled em and hid #2 in his locker. They found #2 as the bell rang to go home and my buddy and I were standing outside our assistant principal's office holding the puppy. He laughed his arse off and didn't punish us.
This same assistant principal wasn't exactly smiling when he found his 90 Mustang GT full of balloons the following week. We put roughly 350 of em in until the last one burst. Funny thing about "a Fox Body Mustang and an inch from the right side of the driver's door handle, with a screwdriver". CAP prolly knows what I'm talking about.

But while he was pissed of the mess it caused, later on in an encounter shopping, he still laughed his arse off.
Finally to further piss off a good friend of mine, we "bounced" his Chevette perpendicular and two buddies cut it close. Bell rang, he sprinted for the parking only to use damn near every cuss word. We still laugh at that one to this day and the urinal.