be on another planet
be (living) on another planet
slang To be oblivious to one's surroundings or act strangely. I have no idea what the professor said during today's lecture because I was on another planet the whole time. The millionaire investor always says something wacky in the board meetings—it's like he's on living another planet.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
be on another ˈplanet,
what ˈplanet is somebody on?(spoken, humorous) used to suggest that somebody’s ideas are not realistic or practical: He can’t really think we’re going to finish the job today, can he? What planet is he on?
Farlex Partner Idioms Dictionary © Farlex 2017