very foolish, irrational, or strange

everything about the business seems insane

you'd have to be insane to disagree

she called the decision absolutely insane

lacking the ability to think and behave in ways considered to be normal, especially on account of serious mental illness (not in current technical use)

he had gone insane

certifying patients as clinically insane

shocking; outrageous

they were making insane amounts of money

my long-distance phone bills are insane