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'.”
(..) comes out of your mouth is a lie. All I know is that I would have saved myself a lot of suffering, if I'd just given that bread to the pig. I think the only thing left to say is "thank you." I need to be in the capitol. No, you have done your job. You've been very successful (..)2015 The Hunger Games: Mockingjay - Part 2
(..) I remember you in the rain. And I burned it on purpose. To give it to you. I remember my mother hitting me. I was supposed to give it to the pig. That was the first we'd eaten in days. Why would I take a beating like that for you? Because you were kind (..)2015 The Hunger Games: Mockingjay - Part 2