Used mainly in informal situations among friends or in artistic expressions like songs or movies.

Colloquial Usage

Sometimes said sarcastically or humorously about someone's unusual ideas or behaviors.

Sarcasm or Exaggeration

Though it suggests craziness, it is usually not meant as a harsh insult, but as a lighter remark.

Considered slang, best suited for casual conversations and not formal situations.

Often indicates a high level of intoxication or extreme effects of drugs.

Can refer to being under the influence of drugs other than alcohol too.