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'.”
(..) Come on down and dine On this tasty swine All you have to do is get in line Aaaare ya achin' Yup, yup, yup Fooor some bacon? Yup, yup, yup Heee's a big pig Yup, yup, yup You could be a big pig too. Yup, yup Nala, you find my mother and rally the lionesses. I'll look for Scar. SARABIII! Yes, Scar? (..)1994 The Lion King
(..) Good. Now get out. Mm, yeah, but-- we're still hungry. Out! Whoah. Nice one, Simba. Thanks. Man, I'm stuffed. Me too. I ate like a pig! Pumbaa-- you are a pig. Oh. Right. Timon? Yeah? Ever wonder what those sparkly dots are up there? Pumbaa. I don't wonder; I know. (..)1994 The Lion King