Rocking is a pastime known to consume vast amounts of time amongst people who are bored. For those non believers, rocking is like Squash. You build up a sweat for half an hour and try not to get hit in the eye.
Rocking can come in many different forms. The most popular is of the "I can't dance, but if I bounce up and down like a demented chimp for a while, people will think its a dance from my native culture" variety.
Can also be a reason to legimatly beat the crap out of people you don't like, and/or owe you money. see Sebb.