A doofer is an object that is given to the actor to use during the rehearsal for a stage production that takes the place of the actual prop.
For example, a block of wood with a piece of tape reading "cell phone" may be given to the actor while the actual prop is being purchased or created. This block of wood would be called a doofer.
Anglicised pronounciation for a French cooking vessel, a Doufeu (roughly, gentle heat). This is a large cast iron pot, the lid of which is filled with ice or cold water so that the liquid inside condenses and produces a concentrated flavour.
A person who is on welfare or the dole, but is actually quite capable of finding work. He will often fake an injury or illness to substantiate his claim that he is unable to find a job or perform work if a job should be found for him. He finds it more convenient and easy to live on the dole.
What a doofer! He sits around all week watching Emmerdale, and only goes out once a week to collect his dole.