The sign has been honoured with the wackiest consumer warning label of the year award by a group that aims to highlight how the fear of lawsuits is leading to outright stupidity.
Second prize went to a label on a children's scooter that warned: "This product moves when used".
Sponsor Michigan Lawsuit Abuse Watch says its goal is "to reveal how lawsuits and concern about lawsuits have created a need for common sense warnings on products".
Ed Gyetvai from Ontario, Canada, won $500 (£265) for sending in the loo brush label, while Matt Johnson of Illinois won $250 (£133) for his second place entry.
In third place was a warning on a digital thermometer that read: "Once used rectally, the thermometer should not be used orally".
Ann Marie Taylor of South Carolina won $100 (£53) for that gem.
"Warning labels are a sign of our lawsuit-plagued times," the group's president, Robert Dorigo Jones, told the Associated Press news agency.
"From the moment we raise our head in the morning off pillows that bear those famous Do Not Remove warnings, to when we drop back in bed at night, we are overwhelmed with warnings."
However, Joanna Doroshow, executive director of the Center for Justice and Democracy in New York, said such warnings had saved many lives.
"It's much better to be very cautious…than to be afraid of being made fun of by a tort reform group," she said.
