The threads on weed in Texas and property tax on cars in Virginia inspired me to start this thread. Does your state or city have laws or regulations that might catch out-of-staters unaware and get them in trouble?
The list is probably extensive. Left turn on red and Romeo-Juliet laws come immediately to mind.
@skieurope I think you mean “right on red”. Left would be awfully dangerous. 
Every state allows right on red. But only some allow left on red to a one way street.
https://axleaddict.com/safety/Obscure-Driving-Regulations-Ignorance-is-no-excuse
@doschicos Nope, I meant left on red. AFAIK, right on red is allowed everywhere in the US except NYC. If there are other places where right on red is not allowed, then I may learn about it when I get pulled over. 
As an example of left on red, MA allows left on red from a one way street to another one way street; NH does not.
I think state laws vary on whether you can talk on a phone without a hands free device. CA has some odd rules about placement of a GPS or cell phone on the dashboard. And don’t get me started on motorcycle lane splitting - only alllowed in CA, and is terrifying the first time you encounter it.
Can’t do left on red in WA. As an exception, the only time one can turn left on red is when the car already crossed the line (on green) and the driver is waiting for the incoming traffic to allow a safe left turn. So if the light turns red at that point, only one vehicle - the one that legally crossed the line on green - is allowed to turn.
One way streets are treated differently. And they are not that common outside of large cities.
Toooo many crazy taxes to mention in our new town in IL and every possible thing that could be done to a house requires a permit. No plastic bags at the stores unless you pay extra, traffic laws pertaining to alley ways, no cigarette sales for anyone under 21, and I’m sure there are more.
Idaho Stop Law for cyclists. They get to treat stop signs as yield signs and red lights as stop signs. I like it because it promotes traffic flow, but it confuses people who think bikes need to follow the same traffic rules as cars.
Not an actual law, but CA plates in WA are cop magnets.
I think helmet laws for bicycles and motorcycles vary from state to state.
Okay, here is what I didn’t know. In many places, including WA, you can turn left onto a one way street from a TWO WAY STREET. I grew up (in Mi) learning that I could go left on red from a one way to a one way. But it never crossed my mind til now that it is okay from a two way street. 
Unless it has changed, NYC doesn’t allow right on red unless posted that one can do so.
I did not know about the left on red from one way street to another one way street in MA. It makes sense in those circumstances, though.
VA has lots of driving laws that don’t apply in other states. Radar detectors are illegal as well as in a handful of other states. In VA, if you are driving more than 20 miles over the speed limit, or more than 80 miles per hour (this could be on a 70mph highway so only 11 over the speed limit), and you get stopped, you will be charged with reckless driving which is a 1st class misdemeanor in VA, on par with sexual assault and DUI. It’s a very harsh punishment.
Drinking laws vary from state to state. Most states have one or more exceptions to the under 21 ban, for instance allowing kids to drink in their parents’ home in their parents’ presence. Some take it further, allowing it when parents aren’t present, or in a restaurant in their parents’ presence, or allowing underage drinking for educational purposes such as a cooking class.
It has not changed.
Voting laws can vary. In Wisconsin, new residents should learn about voter registration, voter ID, and early voting.
Ha! Growing up in NJ, the police were out in every town on the way to the shore on weekends, stopping PA plated cars.
I’m old enough to remember when turning right on a red light wasn’t allowed. The first time I saw it was when we used to visit Canada for vacations. As with many things, Canada was more progressive. 
For those visiting Ontario, you can drink legally at 19; radar detectors are illegal; only handsfree cell phone usage while driving and next month, marijuana becomes legal.
And nary a single Canadian driver will be brave enough to cross that line, even when the light is green, until they can make their turn.
I think u-turns are not allowed in many places in Canada, or have weird exceptions. I was driving a car load of Canadians, flipped a u-turn, and the collective gasp made me think I’d hit a little old lady
New York’s left turn on red law (one way to one way) seems to read it’s okay except in cities of over a million. Which currently is only NYC.
It used to be quite uncommon for states to have High Occupency Vehicle (HOV) lanes, but I guess it’s not as rare any more. Many areas also allow exceptions, like for “green” cars.
I also remember in Northern VA when people would drive past the Dulles airport to get on what was otherwise a toll road - illegal.