What was (one) thinking?

What was (one) thinking?

Used to express confusion, annoyance, or surprise at someone's past opinions, decisions, behavior, etc. You picked bright, neon-red wallpaper for our bedroom? What were you thinking? A: "What were you thinking, driving so recklessly like that? You could have gotten yourself killed!"
See also: what
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
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