Make a Wish. Have it horribly corrupted.

[iKod]

Granted, but you get smothered by it to death.

I wish for a wish.

[Uncle Garnetto]

Granted, but that wish is also corrupted

I wish I could have mastery over time and space

[Jennythe3]

Granted, but it will tear the fabric of space-time, destroying you.

I wish Pokemon exist in the real world!

[Uncle Garnetto]

Granted, after manky toe your face off. Snorlax eats you.

I wish I had a working ipad2

[Trekkie WhoLocked Fangirl!]

granted, but it is stolen and you go to jail...

i wish for a signed copy of the hunger games

[Uncle Garnetto]

Granted, even better, first edition brand new signed, one of a kind worth millions of pounds... You reach out to grasp it... And spontaneously combust, killing you and destroying the book
Meuahaha.

I wish... For a peice of chockolate cake...

[Jennythe3]

Granted, except the chocolate was made by your dog.

I wish that Latias could breed.

[Sizacu]

Granted, but she can only breed through incest.

I wish for an orange smiley rather than a light green-blue one.

[Spriter]

Granted, but it likes knives. Better run Sizacu...

I wish for some stuff.

[Uncle Garnetto]

granted, you have some stuff that eats all you other stuff, including itself when it is done...

i wish for a grenade with the pin pulled out (it is ready to explode if i let go of it)

[Spriter]

Granted, it explodes a millisecond after you drop it, exploding itself and you at the same time.

I wish for a wish to wish about a wish with a wish.

[OranBerrySandvich]

Granted, but it gets stuck in limbo.
WISHCEPTION.

I wish for  turkey sandwich. No funny tricks though, you hear? Make sure it's a little moist - not soggy.

[Jennythe3]

Granted, but the turkey is still alive.

I wish to not have a corrupted wish.

[Darkwing]

Granted. Sadly the ensuing paradox causes you to marry Simon Cowell.

[Uncle Garnetto]

I wish people would follow the rules and MAKE A WISH!!!!!