From Wikipedia: The Euthanasia Coaster is a concept for a steel roller coaster designed to kill its passengers. In 2010, it was designed and made into a scale model by Julijonas Urbonas, a PhD candidate at the Royal College of Art in London. Urbonas, who has worked at an amusement park, stated that the goal of his concept roller coaster is to take lives “with elegance and euphoria”. As for practical applications of his design, Urbonas mentioned “euthanasia or execution”.
“The Euthanasia Coaster would kill its passengers through prolonged cerebral hypoxia, or insufficient supply of oxygen to the brain. The ride’s seven inversions would inflict 10 g on its passengers for 60 seconds – causing g-force related symptoms starting with gray out through tunnel vision to black out and eventually g-LOC, g-force induced loss of consciousness.
Dunno about you guys but I prefer the Murder Carousel.