Pretty simple game.
Someone makes a wish and as the title says, you ruin it.
eg.
person1: I wish I had loads of money
person2: granted but when you get it the currency it's in Martian Zlotty so it's no use. I wish I had 3 legs.
person3: granted but when you get your third leg, you can't use your other two. I wish I could...etc, etc.
I'll go first:
I wish I could be a comedy writer