What happens if you smoke moldy fruit in a hookah?

Not a good idea: Although you may not get sick from it, you are exposing your lungs to molds which in susceptible people can cause asthma, hypersensitivity pneumonitis (which acts and behaves like pneumonia), and even permanent lung damages with repeated exposure. Hookah itself is not totally harmless and you certainly don't need to add molds to the mix.