A knife catcher is an idiot investor who buys something while its price is still dropping. Usually refers to someone who bought a house that is 'an incredibly good deal' just before it drops another 10 percent. Called a knife catcher as they are trying to catch a good deal, but will just probably lose their fingers as the knife goes whipping by.
Haw Haw Haw! They said I would never be able to sell my house in Florida in this bad economy, but some knife catcher showed up to take the turkey off my hands!