Best one yet!

To do this one right you will need to somehow put the kool aid in a gelcap or something to delay the release till they are in the shower.... if not all that will happen is they will turn the shower on, see the mess and then let it run out or turn it off and never get the stain.

I might be over thinking it here but... to get the biggest bang for the buck.

To lesson your chances of waking up with Mr Happy super-glued to a brick. You might want to consider using a bullion cube on your wife instead of the hair/skin staining Koolade.