I grew up in Pakistan and I’d never heard of the term until I immigrated to the US. Pakistani English until the 1990s was VERY influenced by colonial era British English, with of course lots of localisms and loan words.
I just asked a 25 year old in Pakistan, and he’d never heard of the term.
Isn’t the jump seat just… a jump seat? Like on the bus? Has nothing to do with coaches per se, or the location of the seat.
When discussing the most dangerous seat, it helps to distinguish what era we’re talking about. Before front seatbelts? After front seat belts but before crash-tolerant interiors? After back seatbelts? After front shoulder harnesses? After rear shoulder harnesses? After driver airbags? After airbags everywhere? The era when seatbelt compliance was near zero? The era when seatbelt compliance is very high?
The traditional pre-seatbelt argument for shotgun being extra dangerous was that in any impending collision, the driver will instinctively steer to protect themselves and their side of the car, thereby exposing the right side of the car to the brunt of the crash. That won’t be true in every crash, but in those where the driver has to choose, they’ll choose safer for them. And the people in the back have the soft upholstered front seats to bounce off of, not the solid steel dash and rigid steering wheel & column. So the lose-lose seat is shotgun.
I’d like to see some fresh data including only, say, post 2020 model year cars. That gets us to vehicles with modern highly crashworthy design and also to people with 2020s level of seatbelt compliance, whatever that may be.
We had that same terminology, but it applied equally to the front or back seat. So, three guys: one drove, one had shotgun, and one rode bitch, all in the front seat. What an enlightened crew we were.
Keep in mind, when I was ripping and running as a young man, it was a bench seat, front and back, and generally land yachts were still in style (along with onions on our belts). It was not cramped at all, and nobody got lonely. 
I am old, and we always did.
I heard the bitch seat was the pillion on a motorcycle.
Sounds about right. No sense limiting a misogynistic term to a single vehicle type. 
ETA: Again, what jerks we could be. Sorry!
Back in the 1970s / 1980s ish I recall seeing a crowd photo of some motorcyclists standing around yakking amongst all the parked motorcycles. One hefty bearded dude was facing mostly away from the camera. His T-shirt had words on the back that read
If you can read this the bitch fell off.
I laughed.
Yeah, an enlightened crew to be sure. All of us back then, me certainly included.
To me, jump seats were the folding seats between the front and back seats of a car. The Connallys were sitting in jump seats that day in Dallas.
My family just always called it the front seat. Was surprised the first time I heard “shotgun” (maybe 10 years old?). Grew up on US military bases.
As a comparison, in Japanese it is the “assistant seat”.
I’ve known about “shotgun” since my teenage years in the 60’s. I’d never heard about “bitch” until watching No Country For Old Men when Chigurh meets up with the two guys who will show him the scene of the gunfight. He drives up, as they all get into their car one of them asks Chigurh “Mind riding bitch?”
Figured it out instantly but had never heard it before.
65 here. I’ve never heard of anyone in the U.S. not knowing what riding shotgun was. At least no seasoned adults.
But the guy in the OP is probably no older than mid-twenties and that generation seems to think the world began on the day they were born and they refuse to retain anything about things that happened before hand. I’ve got 2 grandsons like this. It’s irritating and makes them appear stupid.
Is anyone else getting an ear itch for some Jr. Walker & the All Stars?
Ha, yeah, I’ve had that ear worm stuck in my head ever since I started the OP.
I just asked my 15 year old and he knew what it meant. Chicago area.
He’s never really been in a position to call out or claim it, he just picked it up along the way.
I think the first time I ever heard it was in the song ‘Woodstock,’ although I’m not sure it makes a lot of sense.
Sixty-eight years old checking in. I don’t remember hearing it in my childhood (in the sixties), but that’s not to say I don’t think it was in general use at that time. By the time I was somewhere into my teen years, in the seventies, I knew it. But I couldn’t tell you where or how I picked it up.
Whenever my friends and I went for a cruise in high school you can bet “I call shotgun!” was part of the ritual.
Similar age (66) also from Philly are. Familiar with the term since early grade school. Son (31) and his friends were calling “shotgun” when I drove them to and from swim team in high school. Didn’t learn it from me.
I was a kid in the Baltimore suburbs till I left home in '73. On the rare occasions when only one parent would be in the car, we spawn vied to be the first to say “I call front!” I didn’t hear the term shotgun till some years after I’d entered adulthood.