Definition
To behave in a crazy or irrational manner.
He must be off his head to try swimming in this storm.
You must be off your head to believe that nonsense.
She must be off her head to quit her stable job for an unrealistic dream.
To be in a state where one's behavior is uncontrolled due to excessive alcohol or drug consumption.
He was completely off his head last night after drinking too much.
She looked off her head, probably from taking drugs.
The group of young people were off their heads after getting drunk.