The showerhead effect is a disruption in the male urine stream caused by jewelry or urethral cutting. That is, it makes it so you accidentally urinate on yourself if you try and stand to pee. The solution is to sit down to pee.
In the case of piercings, you can try taking the piercing out, but that doesn't always solve it (first picture on the left, above). Nor does flipping the ring around (second picture). Most people eventually accept that peeing like in the third photo is part of the deal when it comes to PA's, and simply start sitting.
Above you can see the effect that subincision has had in two individuals. The first can no longer stand to pee, but the second can. It's largely luck of the draw. Some men choose to carry a small tube which can be inserted into the urethra to guide the urine.