not know the time of day

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not know the time of day

To be completely unintelligent, daft, or not alert. We paid for her to attend the best university in the state, but three years in, she still doesn't know the time of day. How can you expect me to respect my boss when he doesn't even know the time of day?
See also: know, not, of, time

know the time of day

be well informed about something.
See also: know, of, time