One idea for excellent office joke. This year, April 1 falls on Friday so that will certainly be quite happy at the office
For this joke you need less training. You need a cup (outer), C200or similar adhesive, brown tempera paint and oiled (wax) paper.Pour glue into the cup, mix with tempera paint and spill onto the paper cup and add credibility to several packets of sugar and stirrer. Allow to dry - you'll need at least several hours, depending on the glue and then carefully remove the paper.
Take this cup in the office and put it on the desk of a colleague or coworker. Listen and watch the reactions of your colleagues.