Justin Bieber
Did Justin Bieber impregnate his mother? This, following rumors that his mother would appear in Playboy. Playboy actually did approach Mrs. Bieber, but what about the incest rumors? Where did they come from, and why?

What generally happens is that prank-happy trolls on the 4chan image board decide to manipulate Google's "Hot Trends" by searching for a specific key phrase in order to send that phrase to the top of Google's "Hot Trends."

When other Google users see this phrase in hot trends, they too search for it in order to find out what the key phrase refers to. Before long, millions of people are trying to figure out whether or not Bieber impregnated his mom, and rumors fly accordingly. This phenomenon was successfully brought about by 4chan with the phrase 'Justin Bieber syphilis.' And the rumor that Justin Bieber died.

It's not just search pranks. 4chan also tried to send Bieber to North Korea. Why do these people waste time with this stupid nonsense?
Trolling Is Fun
Have you ever done that thing where you tell your friend that there is something on his shirt and then when they look down you flip up your hand and run your finger up and flick him right in the face? The appeal of this pranking is kind of like that.
Justin Bieber Is Easy to Hate
He's obnoxiously adorable. Tween girls love him. His music sucks. He's more successful as a teenager than most of us will be when we die. He's the perfect target.
Sense of Camaraderie
A lot of the people who use 4chan are introverted social misfits. They like feeling like they're a part of something bigger than themselves. Many of these people are students with a lot of free time and endless boredom. Every once in a while this impulse manifests in something positive, like their championing Zach Anner as TV's first travel host with cerebral palsy, but it's usually directed at tearing down Scientology or some bubblegum pop star.