An intensely insane person with manic tendencies. Can also be defined as a person whose lack of sleep has driven them to insanity.
An extremist with a need for chaos.
"That guy just came at me, out of no where. What an insaniac!"
"I think Tim's been up for 5 days now. He's really turning into an insaniac"
"Dude, I'm going skydive-snowboarding tomorrow. I'm a f***ing insaniac!"