Be not right in the head phrase
If someone is not right in the head, he or she doesn't have a normal mental state or condition.
After the car accident, Jane was not quite right in the head.
I reckon that Jenny is not right in the head now, for she drives like an idiot.
She might be not right in the head when thinking of this unrealistic idea.
Very stupid, or silly
A very offensive term used to describe an upper-class British man who is stupid or inexperienced
Stupid or crazy
If you're off your trolley, your ideas or behaviour are crazy or insane.
The verb "be" should be conjugated according to its tense.