imbecile
Definitions
A person who is considered foolish or unintelligent.
A person affected with moderate to severe intellectual disability (dated, offensive).
A stupid or idiotic person.
Examples
I felt like a complete imbecile when I realized I had been holding my phone upside down the entire time.
The critic dismissed the film as nothing more than an imbecile attempt at comedy.
Only an absolute imbecile would try to fix the electrical wiring without turning off the power first.