> what's up with everyone everywhere saying "my God, drivers in [where I am] are the absolute worst"?
I think most of those people have not lived many places. My perception is that there are solid differences in driving culture between some cities. I found San Francisco traffic heavy, but with fairly courteous drivers. Vancouver same. Toronto was atrocious - lived there for ten years and never got used to the aggression and almost sociopathic attitude toward other drivers. Now I'm in Edmonton, where it's back to mostly OK - drivers here are a little more timid than other places but don't lean on their horn for every perceived slight or compromise the whole system to gain a 5 second advantage.
My completely unscientific take is that the most aggravating traffic comes when traffic gets dense enough to be a real irritant (I dunno - say maybe doubling a normal drive time between two destinations), but is still civil enough that most (say 90%) drivers are pretty polite and cooperative. That means that aggressive driving actually pays off, which makes it harder to take for people who don't zip past traffic in the turning lane only to forcefully merge back in.