I guess it's called "jowling," but what it is is a person (or animal in some cases) shaking their head in a manner that causes their facial skin to stretch and flap, and having a photo snapped during the shake.

It's harder to describe than to just look. So take a peek at http://www.jowlers.com for some examples. There are some pretty funny shots. I especially like the "Best Hair Jowl" award on this guy who seems to illustrate the definition of a stoner:

this "Pet Jowl" award of a dog who looks like he was just hit by a train:

and this "Crazy Intense Jowl" award of a guy with exceptional timing on Splash Mountain at Disneyland:


I don't know how many of the photos on that site are accidental, as I'd guess most all were strictly intentional. Not a groundbreaking site but definitely worth a chuckle.