The worst game idea I can think of?
The Wacky Adventures of Arsonist Peepee in: “Running from the German Skunk Fursuit Police while Denying the Holocaust”
Edit: Though to give a more serious answer, there is one that I had. A while back there was somebody on here who kept posting threads about hating Visual Novels, stuff like “what would you do if you found your kids playing them” and the like. So as a joke I started making something called “My Son Will NOT Play Virtual Novels”
The entire thing was going to be an anti-VN where you assumed the role of a father (as opposed to most VNs customizing your persona) dead-set on having his rebellious teenage son be shielded from VNs after they killed the rest of their family. You would have had no outward customization of the characters, but instead your son would react to how you behaved, and that would have lead to different scenarios (i.e. giving your kid a laptop but being strict would turn him emo, and thus he gets into online roleplay and from there writes a VN, leading to a lose-state). And at the end of most of the scenarios where he inevitably picks up a VN, the player/father would enter a minigame where they brutally kill the son in some cartoonishly over-the-top way (i.e. chasing his bike down from the family car lined with nitro, smashing all of his bones in a sumo ring after catching him with an 18+ VN, smiting him with lightning after the VNs turned him gay, etc etc) all while the BG music changes to some crappy screamo of me shouting “I HATE VIRTUAL NOVELS” over and over again. And then for most of the endings would have just been you getting put on death row.
Dropped it after a bit since I’m having a lengthy time making a simpler game than that, so I won’t be upset if someone lifts that idea.