pigs don't fly
a phrase meaning "normal" and "civilized" (however one defines these words) people don't behave the way you do.
Example:
a boy, after having been to physical science class in elementary school and having learned the basics of electricity, tries putting scissors in the kitchen plug.
His mother starts admonishing him:
mother: is this f-sag you twit? what are you doing, you'll create sparks and burn the damn house down. Pigs don't fly. Go to your room now. She then takes a broom and starts chasing him around the house.
son: I can attach balloons to anything i want, no?
a boy, after having been to physical science class in elementary school and having learned the basics of electricity, tries putting scissors in the kitchen plug.
His mother starts admonishing him:
mother: is this f-sag you twit? what are you doing, you'll create sparks and burn the damn house down. Pigs don't fly. Go to your room now. She then takes a broom and starts chasing him around the house.
son: I can attach balloons to anything i want, no?