The Konix Multisystem was such a failure that it didn't even come out.

The Pippin was a rare failure for Apple.

The 32X did little but piss off the populace.

The 5200 was Atari's first real misstep.

The Jaguar CD killed not only itself, but the Jaguar too.

The Phillips CDI was a massive failure for everyone involved.

With Nintendo it's a tie between the Famicom Disc Drive, the Virtual Boy, and the N64 CD add-on.