While not in the OC, I live in a similar upper middle class area and neither of my teens nor their friends carry a knife, to my knowledge. Why not? Well, they'd be in a lot of trouble if they took a knife to school. My son owns a Swiss Army knife from his earlier Boy Scouts years, but it lives on his desk and is basically only used to cut tags off new clothes. The only family member who regularly carries a knife is my 72 year old Dad, who really only ever pulls it out when we need to cut the ribbon off a wrapped gift at family gatherings. Maybe SW was a regular knife carrier post-high school but you can bet that BB wasn't.