lunatic
lu-na-tic
adjective
Extremely foolish, irrational, or wild in behaviour or ideas.
"That's a lunatic idea, mate."
noun
A person who behaves in an extremely foolish, irrational, or wild way.
"He's a complete lunatic, always causing trouble."
Thesaurus
Synonyms: insane, moonstruck, maniac, daredevil, harum-scarum, swashbuckler, hothead, madcap