A recent post has the best of OC & LA county. Which is, in your opinion(s), the worst, should be avoided.
Number 1 on my list:
The Alton Ave bike "path". From Susan st. in Santa Ana to were it ends on Warner. Seems like its always overgrown with weeds, I once picked up 8 thorn punctures on single revolution of my commuter. Add in, glass, water that takes days to drain off, graffiti covered road & walls, meth addicts/strawberry hookers..you get the idea. No one bothers you, but what a lousy path!