soft in the head
Mentally deficient; also, silly, foolish. For example, He's nice enough but a bit soft in the head. The soft in this idiom, first recorded in 1775, alludes to a weakness in mental capacity.
Words nearby soft in the head
soft furnishings,
soft goods,
soft ground,
soft hail,
soft hyphen,
soft in the head,
soft iron,
soft job,
soft launch,
soft lens,
soft line