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'.”
(..) Good to have you back. You all right? Yeah, I'm fine. He's hurt. I am functioning adequately, Captain. In a pigs eye, you are. Captain, we discovered that a stolen artifact appears to come from this planet. Damn it, Spock! - Are there any medical supplies on this *something*. - This way. (..)2016 Star Trek Beyond