A design, action, or decision that is clearly incorrect or inappropriate. Often capitalised always emphasised in speech as if capitalised. The opposite of the Right Thing more generally, anything that is not the Right Thing. In cases where "the good is the enemy of the best", the merely good - although good - is nevertheless the Wrong Thing. "In C, the default is for module-level declarations to be visible everywhere, rather than just within the module. This is clearly the Wrong Thing." [Jargon File]
