(the) elephant in the room
An obvious truth or fact, especially one regarded as embarrassing or undesirable, that is being intentionally ignored or left unaddressed.
We all sat sipping our tea quietly; no one wanting to bring up the elephant in the room about Joel's expulsion from college.

the ˌelephant in the ˈroom a serious problem that everyone is aware of but which they ignore and choose not to mention: The growing budget deficit is the elephant in the room that nobody wants to talk about.

@IdiomsLand