[Vocabulary] a pink unicorn?

[michael147]

He imagines that the Democrats will agree to fundamental reform of entitlements, something they haven't done in, oh, I don't know, 60 years, but we imagine that they're going to, we imagine a pink unicorn.

What's the analogy of "a pink unicorn" here?

Your answer would be appreciated.

 

[SoothingDave]

Unicorns don't really exist, but the ones that are imagined are white. So a pink unicorn is even more fanciful, more imaginary.

The point being that Democrats are not going to agree to reform entitlements.