the elephant in the room

(idiom) a major or controversial problem that is not discussed

Example Sentences:

When I had dinner with my parents, the elephant in the room was the fact that I’m 45 years old and still single.

There was an elephant in the room when I spoke with my mother, because she hates my new boyfriend.

Media:

From the Blogs:

Climategate is the elephant in the room for Obama’s carbon plans

From Twitter:

Similar idioms:

1. paint the town red
2. flash in the pan
3. shell out