No, this will not ruin someone's actual shower in their bathroom, but with the help one Jolly Rancher candy it will definitely ruin their day.
The following article is a great little prank that can be used for April Fool's Day, or you can just use it to get at someone who may or may not deserve it.
Place the Jolly Rancher candy inside the shower head.
Next, unscrew your victim's shower head from the pipe coming out of the wall. You should be able to just twist the shower head until it pops off.
Finally, screw the shower head back into place with the Jolly Rancher candy inside. The next time your victim takes a shower, he or she will become very sticky. Upon realizing this, they may take a second shower, resulting in more stickiness.
The first step of this prank is to find a way to get into your victim's bathroom and be completely undisturbed. This should be easy as long as your victim has some common courtesy and a bathroom door with a lock.