What is the ultimate prank i could pull?

I don't know if this would be ultimate or not, because its not really that creative. But if you are really into getting her back, replace her shampoo (or some other product she uses alot) with hair dye, like a very vivid color like orange. True it's not devious, but she'll have to live with it for a while, and plus the guy that likes her will see it too. Haha, but then again, that's a bit evil.