Be (living) on another planet humorous spoken slang
To be not aware of what is happening around you or think and behave oddly.
They teased Mary because she seemed as though she'd been on another planet when the teacher asked her to solve an easy equation.
You may think that I'm on another planet, but rethink what I've told you. I'm sure you will find it practical. His idea was patently ridiculous. He must be living on another planet!
None
Be ignorant, innocent or totally unaware; not know what's what
To be so confused that one is unaware of one's actions
Used to describe that you are unaware of something or do not find an answer to something.
To be unaware of what is going on around one.
1. To not know or discover that somebody has done something wrong.
2. To not understand something, though it has been explained to you.
The origin of this slang is not clear.
To punish someone or something harshly
He's a really strict teacher, so he'll definitely lower the boom on you if you don't do your homework.