Idiom - "The elephant in the room"

Idiom - "The elephant in the room" - an obvious truth which is being ignored, perhaps because it's a difficult subject. No one wants to discuss the 'obvious truth' (the elephant).

Examples:

"Let's address the elephant in the room, we all know that over Christmas I got very fat, but it's better that it's out in the open and everyone can feel free to talk about it."
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"Is no one going to talk about the huge elephant in the room?"
"What?"
"What your uncle just said! It was so offensive!"
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"Gun control is America's elephant in the room, but they don't seem to want to address it properly"