There are a few people that I know that have the power to singlehandedly render a standard restroom uninhabitable for a good fifteen to twenty minutes after they have made use of the facilities. It doesn’t matter if they spray or light a match, the stench will live on with a life of its own. For such people, there is the Loo Zone Traffic Cone. It provides ample warning that the malignant odors need time to dissipate (even if 10 minutes is not quite long enough to get the job done).

Price: Not available, unfortunately the cones are only being sold by Alibaba at the moment, which means you will need to buy in bulk or wait until someone else does and starts selling them. [Alibaba via Nerd Approved]