I bet it's Ridley Scott's "Alien", right?
Yeah, same here, but in doing research for today's post, it turns out that the "face full of extraterrestrial wang" trope has been around for quite a while. H. P. Lovecraft toyed with the idea in The Shadow Over Innsmouth and The Dunwich Horror although he kept the squick factor on the low side so his works... you know... actually got published. We also see it in A. E. van Vogt's 1939 short story Discord in Scarlet (later included in Voyage of the Space Beagle). Apparently, intestines work just as well as uteri.
In case you're wondering, Alien is NOT the first movie to use this trope. Roger Corman's 1958 B-Movie Night of the Blood Beast has Michael Emmet carrying a whole LOT of alien embryos in his shambling corpse.
Now, our most prevalent image of this trope is, obviously, Alien and it's sequels and spin-offs (and the odd Mel Brooks reference) wherein it's seen as a rape metaphor (and with H. R. Giger at the design helm all we're missing is a handful of roofies). That's where we fall flat as a society because there are quite a few movies that take this and run with it in directions we don't expect.
Alien is the rape metaphor. From there, Breeders and Feast remove "metaphor" from the equation. Demon Seed is an odd duck because it's an artificial intelligence rather than a true alien. While there's no sexual aspect OTHER than pregnancy in Village of the Damned, it's assumed that the creepy kids are the result of alien breeding. Species, another H. R. Giger vision, has pregnancy being the primary goal of these aliens and even the one male example sets off to impregnate as many women as possible (with the women coming to term in minutes...). Xtro gives us a woman implanted with an alien embryo that gives birth to a fully grown man.
And then? Her pussy exploded.
And then there's MY favorite, Giant, Swollen Boob-Monster from Slither.
That being said, it doesn't get used a LOT in movies, but it still leaves a noticeable imprint on pop culture.
Wanna know why?
Sorry. Couldn't help it. Had to be done.
Because most media that contains this imagery is created by MEN and pregnancy is the last great mystery to us. We know how it works, but we don't know how it feels and all we have to work with are Bill-Cosby-esque comedy routines wherein our female companions loudly and sharply blame us for the pain of childbirth (regardless of whether or not we were responsible for said pregnancy) and make dire promises of extreme genital torture whilst demanding the epidural. FOR GOD'S SAKE, GIVE HER THE DRUGS!
As a straight friend once told me, occasionally, vagina looks like a grenade went off in a roast beef sandwich. It scares us. We, as men, don't have a uterus, don't know what it feels like to carry a life inside us unless we've been exposed to a tropical parasite on some kind of EXTREME HIKING TRIP, and, frankly, if we DID, abortion centers would be the new Starbucks. Men are wusses.
This is not to say that Rule 34 is not in effect, here. M-Preg fan-fiction DOES exist. I will not provide links. I'm kinky but not THAT kinky. If you want to subject yourself to it, that's totally on you.