At least they're harmless. Some fruitcakes out there actually believe they can survive on the "life force" of the world alone and therefore don't need to eat or drink anything ever. Here's one of many pages on it.

[edit]Oh. Here's a good one. No food since 1993 apparently and for the low low price of $19.95 she'll also tell you about immortality and various tools to stop the aging process...[/edit]