afflicted with or characteristic of mental derangement
"was declared insane"
"insane laughter"
very foolish
"harebrained ideas"
"took insane risks behind the wheel"
"a completely mad scheme to build a bridge between two mountains"
Exhibiting unsoundness or disorder of mind; not sane; mad
"After losing his job, staring at the wall for hours and talking to invisible coworkers, everyone agreed that something was truly insane about him."