Campers are some of the most loathsome creatures (haha, I called 'em creatures. Nah, you're cool. You're just players who hide behind stuff and wait for people to run along) in online first person shooters. They hang around, lying in wait for unsuspecting players to run past so they can blow them away with their close range weapons or worse yet, they hide in hard-to-reach places and snipe from the safety of both distance and stealth.
In Battlefield 3, a special breed of campers who hide up on the cranes in some of the maps which feature cranes (as the bigger maps are known to do) are known as cranecampers, and they're hard to kill simply because they're in those hard to reach places. Even if you know where they're hiding, it's hard to get a lock on them before getting your brains splattered all over the place.
To that end, sSantzuu put together a little guide (Okay, it's not really a guide) for killing these pesky terrorists who find ways to spawn onto the crane by placing a spawn beacon. Their guilelessness and over-reliance on the safety of their crane leads them to feeling a false sense of security—so he kills them one by one as they spawn in the area repeatedly.