Ombongo

A reply to a statement implying that what was said is an untruth.
Does not need to be used as a response only to untruths but can also be used to point out ridiculous or silly statements which may or may not be true.

Person 1: " 'Got milk?' was my idea!"
Person 2: " Ombongo!"

by Aluvia Saccharide December 1, 2010