I don't have a lot to say on this matter, except "Use your heads" when pulling pranks. There are many more imaginative ways to prank someone then to screw with their gear. As far as I'm concerned, screwing with gear not only lacks imagination, but also smarts. Gear is only manufacturer guaranteed if it is not tampered with and is in it's proper working condition, not full of cream, or oils or sand or bottles or whatever else someone feels fit to put in gear. Insurance companies are pretty picky when it comes to paying out claims and covering wages. I've seen men with "Smokers cancer" who never smoked a day in their lives not covered, how on earth do you expect them to cover a broken ankle because you slipped in the shaving cream in your boots?
Be careful, have fun, but don't compromise safety. Come up with something imaginative!
Oh, and don't mess with my food!! ;)