It's an informal phrase that might be offensive; use it carefully depending on your company.

Use Caution

The phrase often conveys strong feelings about someone's behavior, usually disapproval or shock.

Emotional Punch

Avoid this slang in formal contexts; it's suited to casual conversations among friends.

It implies excessive use of drugs or alcohol, not just a mild influence.

Use the phrase with friends. In formal or professional settings, it's inappropriate.

Use it to describe someone's state at a specific time, not their overall character.