Always steal the whiteboard markers.
Whiteboard markers are, in some office environments, worth their weight in gold. The best attribute of the mystical white board marker, is its ability to disappear when needed. Those who use whiteboard marker also have an interesting habit of never ensuring they are available until the very minute the markers are required. This will inevitably lead to wasted meeting time, as individuals scramble to find the resources they should have had in the first place.
For a next level prank save all of the old dried out whiteboard markers. Keep these on hold to replace new markers with. This method allows for targets to feel safe that they have the necessary tools for their presentation/meeting before it starts. Individuals that are very organized will check to ensure the whiteboard markers are accessible; however, they are not often prone to checking if the markers actually work. This will leave your target standing in front of their audience, scrambling to find a marker that works. This will show the targets clients that the company can not keep necessary supplies in stock. Will this raise questions about the reliability of the company? One prank monkey hopes so.