can't find butt with both hands

can't find one's butt with both hands (in broad daylight)

Sl. is stupid or incompetent. (Use caution with butt, which is often considered crude.) Why did they put Jim in charge? He can't find his butt with both hands! Tom: Jane seems like a bright girl. Bill: You've got to be kidding! She couldn't find her butt with both hands in broad daylight!
See also: both, butt, find, hand