There's certainly been some awful games produced over the years. The Full House, Kojok and Beverly Hills 90210 board games come to mind. However, I think it's unfair to call games like these the worst. After all, if you were a fan of those shows, you might have actually enjoyed them. I'm looking for games that are horrible by any standard.
I've come across a few vintage games that seem beyond the pale. They're so bad, I can't conceive of a human being of sound mind enjoying them. For instance, the French cheese card game...
"I've got 3 Roqueforts and 2 Pouligny-Saint-Pierres. Read 'em and weep."
"Not so fast, son. I've got hand full of Crottin de Chavignols and Neufchâtels. I win!"
I'm not going to sit here and insult old electronic games - they were fun when they came out. It's only in hindsight that they seem cheap and antiquated. Once upon a time, Pong was the coolest game in town. It's unfair to judge it by today's technological advancement.
That being said, The Electric Stockmarket game looks mind numbingly awful. I have no idea how it worked, but I can pretty much guarantee it was not a "game for partytime".
Even worse, it "teaches serious safety lessons without being scary." Wasn't that the fun of those old horrific safety films? Sure, I had night terrors and developed an anxiety disorder, but those safety videos were awesome.

I'm no expert, but I can pretty much guarantee kids don't like to look for good deals on sweaters. In fact, I wonder if there's anything on planet earth they would LESS like to do.
Here's a few more games I found to be particularly horrible. I should mention that I actually owned the Bermuda Triangle game, and it was bad..... real bad.
I can't decide if the Japanese Batman/Flipper looks to be the worst game ever made or the best. One thing's for sure - it's one of the oddest.