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'.”
(..) Our bodies come and go, but this blood is forever. I'm gonna remove your gag, but if you make so much as a fucking peep I'm gonna cut you like a pig and make you eat your own fucking intestines. You got me? Why are you doing this to me? - Why are you doing this? - Doing what? (..)2003 House of 1000 Corpses