I was shocked last night, more than I have ever been in my entire life, that my own mom had never ever heard of this phrase.
Um…am I missing something? 
How, in 55 years of living, could she have never heard this phrase before? I almost thought she was joking at first, but no…she was quite serious.
She had to ask my brother (who had said it, jokingly) and I what it meant.
Huh. Maybe it’s not as widely known as I thought it was…
Front seat passenger position, came from the old stagecoaches where that person carried a shotgun to ward off bandits.
Yup. My husband and I still call it, even though of course we always get shotgun by default. It just feels gooooood to call shotgun.
ETA USA, grew up northeast, now in CA.
Of course. The intricacies lie in when it can be called, and for what time period.
I only started hearing it recently. Maybe ten years. It wasn’t a thing where I grew up, but it’s become widely known, probably from US pop cultural influence.
It was standard when I was in high school in the 60s. I’ve seen it frequently in movies and TV shows; it is a pretty well known phrase.
Yes, of course, and I was aware of the etymology. I don’t use it very much, though.
You’re in Aus, right?
Last 20 years, I’d say. It really became prevalent in the late 80s/early 90s IIRC. I was aware of it as a kid of about 10 or so, and that was 1994.
I’ve heard it since the '70s along with the term for sitting in the middle: “Riding Bitch”
I don’t recall ever hearing it.
ETA: On seeing the thread title, I thought it might relate to speculation about the reason for an otherwise unlikely wedding.
I know what it means, but I have never used the phrase myself, nor have I ever heard anyone say it in real life.
ETA: What I have said, and heard, throughout my life was the much more straightforward “I want to sit in front!”
Heard and used it (occasionally) all my life. On the other hand, I recently used it in speaking to an older guy here in Dallas–in his 60s, I think–and got a confused response. He thought I was referring to the actual shotgun which happened to be in the back seat of the truck.
Oh, yeah. Central US. Often just, “Shotgun!”
All my life. I can’t even remember the first time I heard it.
Two rules:
You can’t call “shotgun” until the entire party riding in the car has stepped over the threshold of the establishment you’re leaving… with both feet.
If you call shotgun too early, you’re disqualified.
I’m about ten years older than the OP’s mother. I know what the phrase means, but I haven’t heard it very many times over the years. I think “riding shotgun” is more common than “calling shotgun.”
I know it and used it in New Zealand, but only after hearing it from a friend.
Same age as Idle Thoughts’ mom. Yeah, I’ve heard “shotgun” for as long as I can remember and I know what it means.
I know it, and it seems like I’ve always known it although that can’t be true. But my husband had never heard of it when our kids started using it.
(He was an only child. So was I, but I had a lot of cousins. I think I must have learned it from my cousins, because “shotgun” is not something only children need to know.)
I’m about the same age as the OP’s mother, and I know what it means. I first heard it sometime in the 80’s I think, probably in a movie. I knew what it meant then because I was familiar with the idea of “riding shotgun”, which comes from old stagecoaches, but was meant more literally originally. I think somebody could be said to be riding shotgun if he was staying near you and protecting you somehow. But then it started just meaning to sit in the front seat next to the driver.
In the 70s I grew up trying to be quicker on the draw saying this than my siblings anytime the kids and one adult set out for somewhere. It was pretty much automatic that a second adult would ride shotgun if two or more were going so in those cases nobody bothered trying to call it. In addition to the main rule of having to be outside the house as stated above I remember a variation where another could challenge the call by beating the original caller in a foot race to the front door of the car. This sort of defeated the purpose of calling shotgun, but provided a second chance at that coveted spot in those cases where there were accusations of false starts to the door and early calls and such.