Unscrew the showerhead and insert several tablets of blue dye. Easter Egg dye might work, but you want to make sure that it's very concentrated. Also, if possible, find a dye capsule that takes a couple minutes to dissolve before releasing the dye. That way, in case the victim turns on the water until it heats up, they won't notice the color. Then, when the dye is released, it will cover them head to toe in blue dye that shouldn't wash off for a day or two. If you're lucky, they'll have their face in the water with their eyes shut, and they'll be extra smurfarific!
It’s Cyber Monday on WonderHowTo! Don’t miss out on all the big sales in the Gadget Hacks shop and Null Byte shop. Use code CMSAVE20 to save on everything, and use CMSAVE40 for all things apps and software. For online courses, apply code CMSAVE70 for the biggest discounts.