off-limits

Adjective

1. Not to be entered or used; restricted.
   • The pond was off-limits to swimmers.
   • Irregardless, ex-boyfriends are just off-limits to friends. I mean that's just, like, the rules of feminism. - 2004, Tina Fey, Mean Girls, spoken by Gretchen Wieners (Lacey Chabert):
   • According to Yang, the six islets have been purely military for more than five decades. "These islets were completely off-limits to civilians, even to Kinmen residents," Yang said. - 2004 October 18, “Kinmen seeks to...