s. m. c. back-clap

Stands for Simultaneous Mutual Companionable back-clap, and is used to describe the warmly-affable gesture that two super-sociable best friends (usually two cool dudes, but hot chicks occasionally share one, too, or a guy and a sturdy-figured cutie) perform to signify an agreement, encourage each other to begin a boring/difficult/disgusting task, start off on a stroll together, etc. It simply involves exchanging a huge beaming ear-to-ear grin, then putting an arm around each other's shoulders and landing a good-natured thump on the back to indicate their hearty positive feelings and congratulatory appreciation for each other.