My vote would have to be in CostaMesa/SantaAna Sunflower Ave. between Main St. and Bristol. That section is riddled with rough pavement, loose gravel, and cracks. The section of Sunflower Ave. between Bear St. and Fairview has good pavement, but gets debris from the trees, as well as a "pinch point" where two traffic lanes become one. If you are riding more than 3 feet from the curb, you can get taken out by drivers who don't realize the road becomes narrow at that point.
Another bad bike lane is in Newport Beach. Irvine Ave, between 15th and Cliff. This bike lane is in a residential district. There are cars parked ON the bike lane all along this stretch. How can a bike lane be a bike lane when the city allows residents to park on it?