I don’t know if the Darwin Awards have a category for industry enabling, facilitating and encouraging the improvement of the gene pool. If so prime candidates would be Smart for their little two person car and B & Q for their range of chain and bench saws.
For a runner up I would like to nominate Tesco for their “Spa Invigorating Bath Jet.” This device which looks like a cross between a fish tank filter and something that Ann Summers might sell is designed as a bathroom accessory to simulate a whirlpool bath. I am sure that it is safe and the instructions are “adequate” but it is just asking for those of pale complexion and intelect to run an extension lead (available on a nearby shelf) into the bathroom to plug it in.