nutjob

noun

a person who is considered crazy, eccentric, or mentally unstable

Usage: informal; slang; derogatory

Examples

He drives like a nutjob, speeding through every intersection.
My uncle is a total nutjob—he thinks aliens are monitoring his thoughts.
That nutjob tried to climb the water tower last night.
She's not a nutjob; she's just creative and unconventional.
The nutjob at the corner keeps yelling at invisible people.