Uhhh.
One time I used hair chalk to "dye" my hair blonde for a cosplay, seeing as how it was apparently impossible to find temporary dyes for natural hair colors.
Like, you wanna have red, blue, or green hair for a day or two? That's cool, they make temporary dies you can use that'll wash out easily with shampoo. Perfect for costumes and similar special occasions. But -- you want hair that's blonde, or any other natural color? Ohhhh then you have to go through the trouble of getting a "permanent" dye that won't go away until your hair completely grows back into its natural color, which would leave you in a messy transitional state for who-knows-how-long. Temporary dies for natural colors are just not a thing. You either get anime hair for two days, blonde hair forever, or no change at all. ...Thankfully, the chalk sort of worked at getting the same effect.
*cough* Anyway, that's about the craziest thing I've ever done with it. My hair's too untamable to do anything outside the norm and still have it work out well. I can't even have bangs -- I'd just have fluff in front of my forehead. >_>