happy-go-lucky person; dreamer; someone with their head in the clouds
Derogatory slang for a person who is unrealistically optimistic or naive, as if their brain is a field of flowers. Often used critically to describe someone who ignores reality.
That person is such a dreamer that realistic talk doesn't get through to them.
彼女の脳内お花畑な発言には呆れてしまう。
I'm amazed at her head-in-the-clouds remarks.
Standard spelling; the お is a polite prefix, so お花畑 is the natural form.
Variant using the kanji 御 for the honorific prefix; very uncommon.
Literally 'flower garden inside the brain'. The phrase is a metaphorical, idiomatic expression that likely emerged in online or youth slang to mock someone whose thoughts are as carefree and unrealistic as a field of flowers.