Addendum: I am an asshole. My favorite tool-- and I did mean to use that word-- is confetti. One does not fully respect the destructive nature of these small pieces of paper, or if you're really heartless, foil, until they experience the perennial asswhopping that this common party decor can bring to their environment. You will not comprehend the full impact of what I am obviously about to propose until you do it yourself. This is simple:

Confetti's the prank that keeps on giving. Buy several, and by several I mean about a dozen, packs of confetti. It does not matter which kind, but keep in mind that your victim will be seeing these reminders of their vulnerability for the forseeable future, so if you can get it in colors like hot pink and yellow, this is obviously preferred. My favorite targets are the victims' cars, because generally the cleanliness of such is a source of pride, but confetti is equally as annoying if you combine a cracked window, or a lack of door threshold, with a fan. My car was attacked three months ago and its still giving birth to reminders of why I hate the people I work with.

Really, dollar-for-dollar, and after weighing the risk-vs-reward factor, this is the best way to go. I cannot overstate this.