He is a sexist 'pig'. = He is a 'male chauvinist pig'. [=he is a man who thinks women are not equal to men]
The train station will be renovated 'when pigs fly'. [=it will never be renovated]
“This time I think he'll ask me to marry him!” “Yeah, and 'pigs might fly'.”
(..) - He's above the Capitol. - Ow. You are going to be on the hot seat in there, June bun. I grew up on a farm. I know how to wrestle a pig. Do you know the oldest lie in America, Senator? It's that power can be innocent. Good luck. Freddy, good to go. (..)2016 Batman v Superman: Dawn of Justice