They needed to fill a room, drawer, cabinet, locker, car, etc with items as a prank. The winning group would be allowed to pull off the prank.
The standards for this prank were Geometry-based and dealt with volume and surface area. But the main thing we had in this project was authenticity and voice & choice.
Those kids had a definite purpose in calculating how many balloons would fit in a teacher's car or how many marshmallows would fit in a desk drawer.
As April fools day approaches I am reminded that PBL projects don't have to be mundane and boring. If you can't come up with ideas ask your PLN or, even better, your students for ideas.
If you need help thinking of practical jokes just google "pranks," or "office pranks," or other words that will head you in the right direction. But, better yet, just have your students create a prank that requires math to calculate and won't hurt anyone (other than maybe some pride).