My school has pranks every year. I only remember a few, though.
One involved spray painting a large penis on the football field. I'm not sure about this, but I vaguely remember talk about people trying to cover it up by turning it into an elephant.
This year it was was nude streaking with masks. I didn't see it, but I know people who did it.
Last year it was gum in all of the door locks. Actually, I don't even think it was a senior prank. People were just bored.
And the last was a classic for the school. Some seniors brought a junked car inside the pool gates and completely submerged it. I have no idea of the aftermath from that, since it was way before I even got to high school.