pigs might fly nonsense, and miracles may happen

"The management might offer us a decline to pay rise." "Pigs might fly!"

buy a pig in a poke (without seeing the real thing) and buy things indiscriminately (at a loss)

You'll have to show me the car; I don't want to buy a pig in a poke

English proverbs related to pigs

I learned a long time ago that you should never fight with pigs. Because you'll get dirty, and pigs like you.

I learned long ago, never to wrestle with a pig. You get dirty, and besides, the pig likes it