Whenever you see questions being repeatedly tagged with the wrong or incorrect tag -- or multiple tags that mean the same thing -- it's a good idea to propose a tag synonym. The goal is to avoid manually editing the tags on every post by making the retagging automatic for common tag mistakes.
While the-key started out as an April Fools' joke, people are now working to create such a device, and by making it a tag synonym, not only is that a misuse of tag synonyms, but it's calling it an April Fools' joke, and only that, despite its great potential, and there are on-topic questions you can ask on MSE about the-key. Why would this be added as a synonym?
How often do people actually copy and paste from Stack Overflow? Now we know is a perfect example of an on-topic question that could use the tag on MSE. There are several others that are relevant and it doesn't make sense that this particular prank is a synonym.