head in the clouds, have one's

Be absentminded or impractical, as in She must have had her head in the clouds when she made the reservations, because they never heard of us, or He'll never be able to run the business—he's always got his head in the clouds. This idiom uses in the clouds in the sense of “fanciful” or “unreal,” a usage dating from the mid-1600s.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.