9. The To-Do Tattoo
This invention was meant to be a handy and innovative way to quickly scribble a list with a special ink pen on a lined temporary tattoo you place on yourself. The inventor failed to realize that anyone who has time to put a temporary tattoo on themselves, wait for it to dry, and then write on it — definitely has enough time to write a real list on a piece of scrap paper like a normal person.
In fact, it might be so much more work than scribbling on scrap paper that people may just go back to writing on their hands with a regular ink pen like before. Or commit to an actual tattoo, like below.