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'.”
(..) One two three four One two three four One two three four -Rushing or dragging? -Rushing. So you do know the difference! If you deliberately sabotage my band, I'll fuck you like a pig. Now are you a rusher, or are you a dragger Or are you gonna be on my fucking time?! I'll be on your time. (..)2014 Whiplash