bananas?
Cutting sarcastic putdown used by a maths teacher, when a pupil answers a question without stating the units.
TEACHER: "what's the volume of a cube with sides of 2cm each?"
PUPIL: "eight"
TEACHER: "eight what? bananas?"
Pupils would often fall out of their chairs and asphyxiate with laughter.
written by pe*er*tast*, approved by Log

Also accepted as an inherently funny thing, like bananas are, are elephants. Hence "Eight what? Elephants?"
Reminiscent of that stage of mental development when simply saying "mango" was funny.
written by Ch*rlie *ebb, approved by Log

A further alternative was:
Pupil : Sixteen
Mr. MacPherson : You nit!
Pupil : Sorry, sir - sixteen Joules
Here, the amusing similarity between 'unit' (the missing unit of measurement) and the ludicrously mild term of abuse 'You Nit' assured hilarity. *cough* As did said Mr. MacPherson's habit of calling Richard Williams 'Willy Bums'.
written by Ji* Aitk*n, approved by Log