it's not on
be not on
To be inappropriate and/or unfair, as of one's behavior. I'm sorry, but it's just not on to spread gossip about someone.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
it's not onit's impractical or unacceptable. informal
Farlex Partner Idioms Dictionary © Farlex 2017