n. When an intended solution makes the original problem worse.
2016
The cobra effect is a well known term in behavioral economics, referring to an anecdote from British colonial rule in India. The story says that a British governor, wanting to eliminate the cobra population in Dehli [sic], declared a bounty for each dead snake. To his horror, illegal cobra breeders began popping up all over the city — raising the snakes, then killing them and collecting the money. Realizing his mistake, the governor ended the bounty in order to stop the breeders, which caused them to release their now worthless animals into the city, exponentially increasing Delhi’s cobra problem.
2015
Opponents of our chief executive, Leung Chun-ying, should bear the cobra effect in mind.
2014
American sociologist Robert K Merton, popularised the law of unintended consequences and was known as the godfather of the focus group. One of his terms, called the "cobra effect", stresses the perverse effect, which is completely contrary to what was originally intended.
2002 (earliest)
The short term effects of not prototyping can appear to be highly beneficial. After all, our groups seem to grow by leaps and bounds. What, though, is to be said about the long term effects if we fail to prototype? The consistent result is that the church is fatally bitten by the "cobra effect".
The origins of this term are well explained in the 2016 citation, although I should note that there is no proof that such an event ever occurred. A similar event involving rats in Hanoi did happen, so this variation on the theme of unintended consequences is sometimes called the rat effect.