Make a Wish. Have it horribly corrupted.

[Pandemonium]

granted, but they're the size of planetoids and accidentally sit on you

i wish for my wish not to be corrupted

[Alexi: Crazier by the Day]

Granted, but the person who granted it is a liar and corrupts it anyway.

I wish my house had a swimming pool out back.

[master1]

Granted. *moves your house to the hottest part of the Australian outback and puts a tiny swimming pool next it*

Yay! 

I wish I knew Japanese.

[Pandemonium]

Granted, but you are now both unable to speak and incapable of writing :3

I wish for the power to lift a finger.

[Boggypete]

Granted but you now have to spend the rest of your life lifting fingers for lazy people.

I wish I had a horrible painful disease.

[Webby]

Granted. You have a horrible disease in a jar, which will poison the world's population minus you if released.

I wish I wish I was a fish.

[ShinyKecleon]

Granted, but you're a Magikarp holding an Everstone.

I wish that I could go to DisneyWorld again 

[PokeSurfer]

Granted, you have a job there cleaning the toilets.

I wish I could spell any word backwards immediately.

[Alexi: Crazier by the Day]

Granted, but you spell a word backwards for the mayor and he sends you to Venus because you are an alien.

I wish it would snow. Right now.

[PokeSurfer]

Granted, but it snows yellow snow.

I wish I had a crate of cans of Diet Coke.

[master1]

Granted, but you get brain cancer becuase Diet Coke does that. <3

I wish I woke up at 9AM this morning and stayed awake.

[Boggypete]

Granted but now you can never fall asleep again.

I wish everything costed less.

[Zy]

Granted, but everyone in the world now has less money proportionate to the deflation in price.

I wish females don't go through menstruation.

[Boggypete]

Granted but now males experience it instead.

I wish I knew how I felt about my new haircut.

[Zy]

Granted but now males experience it instead.

I wish I knew how I felt about my new haircut.

I can live with that.

Granted, but then you end up getting another haircut.