a humbug
A German word that means nonsense, and if you say it loud enough, it might wake up the ghost of your last math teacher.
I told my brother, 'Humbug!' after he tried to convince me that 2 + 2 = 5 just to get out of doing his homework.
My teacher said 'Humbug!' when I turned in a poem about dinosaurs wearing hats instead of a math test.
My friend said 'Humbug!' when I told her my pet goldfish is a wizard.