You know you're really late to the party when you learn about a new trend in youth culture from the Times' Sunday Styles section. Sadly, that's what happened this weekend when I read Guy Trebay's article on "jerking," a new dance craze that's apparently burst out of Los Angeles via the internet. On the upside, the new knowledge answered a question I'd been asking my television machine for the past few weeks. This was: What is that spastic karate-chop shit the crazy-haired girl in those "All You Need is Love" Blackberry commercial is practicing in front of her bedroom mirror? READ MORE 15