The rules are simple and the results are always terrible in the best way. The person above you makes a wish, you grant it but twist it horribly, then make a wish of your own for the next person to ruin
Keep it clean and keep it clever, the best corruptions are technicalities rather than random cruelty. A wish for a million pounds granted in pennies delivered to your lawn is the classic template to aim for
I will start us off. I wish for a fridge that never runs out of my favourite food