My cubicle was across from another auditor who never cleaned the hot cocoa remains out of her mug before she left on her extended out-of-town assignments. Audit after audit I had to smell her spoiling cocoa and would have to hear her return to shriek “Ewww! My mug is growing something!!!!!” Yet again she exited for a three-week audit and I checked her office and, sure enough, she left her cocoa leftovers in her mug to fester.
Just before she came back, I rinsed out her mug, planted a live moss plant in it, and placed the mug on her desk. When she returned from the audit the subsequent week, she entered her office, put down her briefcase, sat in her chair, and suddenly blurted out in an awed, amazed sort of way, “My mug really IS growing something!”
I went over to her office and politely explained I was the culprit. She understood immediately and thought it was quite amusing, and most importantly not offensive, laughing heartily along with me. And from then on she always washed out her mug before she left and everybody seated around her was happier.
(P.S. I mentioned this story to a reporter for The Wall Street Journal and as a result I was featured in the two closing paragraphs of a “Cubicle Culture” article.)