Worst for me was the rural Texas town where I used to live, just north of Fort Worth. Drivers would deliberately try to run you off the road, unless it was a kid on a tricycle or Big Wheel. It was always 20somthing rednecks in pickup trucks, hooting and grunting out the windows like they're reenacting the final scene in Easy Rider. I even knew some of 'em. When I'd see them later I'd say "You know you nearly ran me down the other day." They'd say "Oh, that was you? If I'd known it was you I wouldn't have done that." As if it's okay to run down perfect strangers. They were jerks in high school and jerks in real life, between stints in the pokey for DWI, possession, burglary, and fussin' and feudin' like rednecks.
But that was years ago. Fort Worth has developed into a remarkably bicycle friendly place.
Of my various duty stations when I was in the Navy and bike commuted in the 1970s-'80s, I'd guess Washington DC was the worst, although it wasn't nearly as bad as my former rural Texas town. But I had a lot of close calls, near misses, and at least two hits in traffic around DC, in just one year stationed there.
SoCal was great for cyclists at the time, San Diego, Oceanside and surroundings. No idea what it's like now.