In a poorly lit room, this could be a catastrophically bad idea if the person being pranked has gastroenteritis as the resultant pebble dashing would go far beyond the mere skidmark in pants result that you envisioned would occur ‼️
Planting a garden in a keyboard. Best office prank idea, especially if the co-worker goes on vacation for a week or so. I would use a keyboard that looks like theirs though. That way you don't get into trouble for destroying someone's property.