What was the worst, least fun, classic arcade game?

Frogger was pretty bad. You struggled and then you died.

Dragon's Lair holds a place of infamy in my heart because it was simultaneously extra-expensive (the first game to demand 50¢) and prone to killing you in the first 30 seconds if you didn't have the expected quick time responses memorized. It felt a lot like pulling a slot machine. You put the money in, there's a moment of activity, and then the money is gone. Not fun.