@wyerframeZ on Twitter did a video parodying those CG animations that bowling alley TVs play when you get a strike—specifically it was a porn parody with the bowling ball fucking a bowling pin. This inspired strong reactions and fan art memeing on the subject. Then someone (I think it was @LadyLuckFate on Twitter) was inspired to draw their OC transformed into a bowling pin and showed them in the immediate aftermath of the porn parody (so, inflated with cum). That inspired the other expansions fetishists to make fattened or inflated bowling pins into a spin-off meme.
And of course, that was the version of the meme that crossed over with the pony artist twitter sphere.
Good can we leave?
I learned about it shortly after posting my comment, but thanks for explaining anyway!
Absolutely fascinating and incredibly hilarious