DIY crayola hair. Fun for all, all for fun. It's summer for crissakes.
METHOD I: "The Ziggy"
Ingredients: Hair bleach, Manic Panic dyes
Manic Panic that shit. I suggest picking colors your sister would have liked in the 2nd grade. If you want a pastel-y look, I've heard mixing the color with conditioner to thin it out makes it paler.
METHOD II: "Suicide"
If of course you can't be bothered to go into a store and buy dye, pull a Cobain and soak your hair in a vat of Kool-Aid. This will only work if you already have blonde hair.
METHOD III: "Fuck All"
Ingredients: Colored powder
So for this you can use powdered make up or powdered hair dye (I guess they make that now?). Or try powdered Gatorade maybe. I wouldn't recommend using paint pigment unless you're positive it's non-toxic. Remember kids, cadmium kills. This is easy-peasy, chuck some powder on your head and muss it up and shake out the excess. You don't necessarily need blonde hair to do this, but it will come out way better. (warning: this will stain your clothes and anything else you walk near when you go out, but that can be fun)
METHOD IV: "Last Resort"
Ingredients: Eggs, Spray color
I mean you don't have to use raw eggs to spike your hair, but if you wanna go hardcore "Freaks and Geeks" go for it. The spray hair color is pretty self-explanatory.
NOTE: Whatever method you try, you pretty much have to listen to The Stooges while you do it. Eatshitdye!