the.com/idiocy
Stupidity wearing the confidence of someone who skipped the instructions on purpose.
means Behavior or thinking so foolish it actively defies the available common sense.
from From Greek idiotes, a private citizen who minded only his own affairs — meddling in no public life, knowing little of the wider world. The clueless layman slowly became the certified fool.
Original insultAncient Greeks mocked those who avoided politics
Medical pastOnce a formal clinical diagnosis, now abandoned
Root cousinIdiom shares it — meaning peculiar to oneself