This prank involves swapping the insides of a dry erase (whiteboard) marker with a permanent marker. The markers look the same when applied to the board, but won't erase. It's the perfect prank to break up the monotony of learning discretization or reviewing quarterly statistical analysis based on global distribution deterioration.
You can probably guess how I did this by the pictures and this description, but here's how I did it.
Step 1: Tools and removal
After removing the caps I used needle nose pliers to grip the tips of each marker to remove. Then use the pliers to open each marker and remove the ink reservoir. Carefully swap the insides of each and use the pliers to push the new permanent marker tip into the dry erase marker housing.