One might use the word quack, at high school, to alarm friends that a teacher is approaching and they should stop doing whatever it os they're doing wrong.
If a friend is smoking or on their phone, say 'Quack,' to casually tell them a teacher is approaching.
Mr. quack is the best duck you will ever meet.
He might seem brainless but that is just a disguise he is actually very smart and can kill you in under 3 seconds.
But dont be alarmed he wont. Probably.