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'.”
(..) as to call a dog filthy... but they're definitely dirty. But a dog's got personality. Personality goes a long way. Ah, so by that rationale... if a pig had a better personality... he would cease to be a filthy animal. Is that true? We'd have to be talking about (..)1994 Pulp Fiction
(..) Honey, I'm going to fucking kill you if you don't shut up! VINCENT: Get in here! JODY: Christ. Get the fuck out of my way. Pig. Quit fuckin' around and give her the shot. While I'm doin' this... you take off her shirt and find her heart. (..)1994 Pulp Fiction