This isn’t the greatest ever, but here’s mine:
Why does the Mississippi flow south?
Because Iowa sucks!
Ohio has had so many astronauts come from that state because people are so desperate to get as far away from it as possible.
Similarly:
Q: Why is it so windy in Kansas?
A: Because Nebraska blows and Oklahoma sucks!
Note: I heard this joke a lot during the heydey of the Big 12. Haven’t heard it nearly as much in the last decade or so.
Just remembered a bad joke I heard in high school.
A: What’s the state where they grow all the potatoes?
B: Idaho?
A: And I da pimp! nearby 14 year olds are all suitably impressed by this clever wordplay
Note: I was B, and A was a preacher’s kid.
A: Did Delaware a New Jersey?
B: Idaho. Alaska.
Did you know that New Mexico got its name before Mexico did?
It’s not a joke it’s actually just a fun fact.