Nobody is worse than Boston drivers, and no one road rages like Detroit drivers.
You know what city really needs a sign like that? Friggen Berkeley, CA. Pedestrians there are the most entitled SOBs I've ever encountered.
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Cali drivers aren't actually that bad. There's a LOT of drivers from other countries in NorCal (drivers from India and China especially) who learned to drive overseas and are either too timid to drive in the US, or are used to way different rules of the road. There's also a lot of drivers who didn't get their license until much later in life since driving isn't as much of a necessity in CA, so you have a lot of newer drivers on the road. Those are the people who make up most of the "bad" drivers.
SoCal drivers can be separated by LA drivers, who are all a bunch of entitled assholes who will cut you off and whose commute is WAY more important than yours, and San Diego drivers which also have a lot of self-important people mixed in with a lot of young college drivers, military, and tons of tourists who help gum up the works.