If you were wondering what it actually is, it's just a bunch of wierdos who have nothing to do but find the most weird-ass places to lay face-down. I saw this guy planking on the top of a McDonald's sign once. Just don't plank, it's so stupid and makes you look like a loser. Don't even get me started with owling.
Planking is a great pastime for people who get bored easily and have friends willing to take pictures of them looking like retards. Public planking is more adventurous and is harder to pull off especially on things like: cop cars, public toilets, and in the middle of six way highways.
Planking can also be dangerous if performed: in places of frequent use, the tops of tall buildings and placed frequented by pedophiles and rapists.
Sexy chick : "Nice! I am spastic eagle planking!"
Dude : "You gotta teach me that one"
Proof that literally ANYTHING can catch on if enough idiots think it is "cool".
Hipster 2: "DUDE! I was planking on some benches at the quad yesterday!"
Normal person: "You guys are fucking stupid."