expression
crazy deed; act of sheer madness; the height of madness
Colloquial expression used to describe an action or situation that is so extreme or irrational that it seems insane.
こんな計画を立てるなんて狂気の沙汰だ。
Making a plan like this is sheer madness.
彼が全財産を賭けるとは狂気の沙汰としか言いようがない。
There's no way to describe him betting his entire fortune other than as an act of madness.
Compound of 狂気 (madness) + の (possessive particle) + 沙汰 (affair, matter). The phrase literally means 'an affair of madness' and is used idiomatically to express extreme irrationality.