The Toronto Maple Leafs have not won a Stanley Cup since 1967, when the NHL had just six teams, and not only that, but a team that didn't exist when the Leafs started building their current roster has already won one.
When something is self-evidently bad, and then made somehow worse by circumstances that are not only ridiculous and stupid, but also extremely unlikely and improbable, and which could only reasonably happen to the Toronto Maple Leafs, then that is when something is "Leafy."
The Golden Knights winning the Stanley Cup was already one of the Leafiest things to ever happen, but being as we are talking about the hockey team from Toronto, I can use it as an example and not even include it in my top-ten list!
That's Leafy in itself. You could even dig down deeper and suggest that the Leafs could have had Alex Pietrangelo as a UFA instead of John Tavares, and had they chosen differently, perhaps they would have won that Stanley Cup instead. It's Leafs-ception!
Other examples of Leafy things that won't even make this list: Not appearing in the Stanley Cup Final since there were six teams; not winning a scoring title, Norris Trophy or Vezina Trophy in the same period; having more players from Ontario play in the NHL than any other place in the world, but still failing to ever win, etc. Then there is Harold Ballard - there's probably another ten or twenty Leafy things that guy alone caused, but most of them were before I was watching hockey.
By now you get the point, so here are the top 10 Leafiest Things to Ever happen.