“Dude imagine jerking it and you cum and a cloud of spores farts out of your dick. They remain airborne and impregnate anyone who passes through your seed-cloud.“ I was on reddit and saw this gem. Not sure if I will actually use it but it is amusing. You could easily have an accidental pregnancy plot.
“That sperm were the size of tennis balls and would burst forth from the head of your penis if you "slept with a woman", slither across the bed up into her, and make the baby. Thanks facts of life popup book with no adults willing to clarify that the objects within were not always to scale.” Here is another from the same thread but worse.
“ Sperm spores, weirdly enough, are stored in the whites of your eyes. That's why older folks generally have poorer vision, there's less material holding their eyes in the proper shape. Anyway, if one of your eyes are ever destroyed, you'll release a huge cloud of spores, which will likely impregnate dozens of people in like a two-block radius. It's nature giving you a consolation prize. You're blind and will soon be eaten by a bear, but your genetics will live on.”
“I used to think sperm was a giant meat stick that split out through the dick hole like a second penis and rubbed inside the vagina until it got pregnant, and then went back into the dick. I had a fucked up mind as an 8 year old.“
I can think of a dream I had about genital transformation that would also fit, but it's too cursed. It's all so cursed!
A couple things this reminds me of. The first and most blatant example is Dwarf Fortress. Every race in Dwarf Fortress reproduces via Spore Reproduction. If there's an adult male on the map and an adult female of the same compatible species, then she will get pregnant eventually....at least that's how it worked in older versions of the game. Nowadays it seems as if they do need to be on adjacent tiles. Also Orks in Warhammer 40k also reproduce via spores...although in their case, it's more of a fungal kind of spore than anything in particular.
The idea makes it seem like the spore cloud is very thick and it would be visible. It still would makes sense that normally you would need to ejaculate inside a girl but it would greatly increase the chances of getting a girl pregnant without penetration.
Combine this with the "Lack of time travel stories" thread -- someone steps on a butterfly in the past, and comes back to the present to find out that their girlfriend now wants his penis nowhere near her, especially not in the place she thinks of solely as her birth canal.