Much of The Witcher's lore is built around the Conjunction of the Spheres, a cataclysmic event where two worlds briefly became one. This Witcher 3 glitch is kinda like that, only it's in a brothel.
Playing the game on PS4, Dirk1nator ! interrupted one of Ciri's flashback sequences to go and visit a brothel, which you're not supposed to do as Ciri, since those instances are designed mostly for some linear combat runs.
Remembering that this house of ill repute is pretty wonky to begin with, when you throw in an extra character the game promptly shits itself.
Once a sex scene kicks in, sometimes you're Geralt. Sometimes you're Ciri. Sometimes, as is fairly common in this brothel at the best of times, you're missing body parts. A lot of time you're both characters at once, the game going all Jeff Goldblum and combining player models.
Here are some SFW highlights, should this sound like your fetish.
And here's the NSFW video, should this actually be your fetish: