Killer Frogs in Frogs
In the 1972 schlock-fest Frogs, stupidity gets amphibious. After a Florida plantation owner sprays his farm with a mysterious pesticide, the farm gets overrun with giant frogs, and there's not a whole lot more to it than that. The film actually ends (SPOILER ALERT!) with a victory for the frogs, which is exactly what humankind deserves for coming up with a movie this stupid.