The phrase "pink elephant" means to imagine or visualize something that is unlikely or impossible to see, usually as a result of hallucinations, dreams, or imagination. Full definition
It was very British, with little knitted pink elephants for aliens, but even at age 3 I would close the curtains and watch. (discovermagazine.com)
Imagine that a large pink elephant walked up to you right now and started staring at you. (premierchristianity.com)
Finally, there's no way to address the 2018 smart speaker market without mentioning the big pink elephant in the room — or rather, not in the room — the Apple Homepod. (digitaltrends.com)