Leeroy Jenkins is a video that has stood the test of time. What is it, exactly? It's a bunch of players in World of Warcraft standing around, planning to go into a problematic room filled with flying enemies when...well, you just have to watch.
The idea of someone pulling a "Leeroy Jenkins" and completely ignoring the plan and just diving into a situation guns-blazing, imperiling their teammates, has now been used in classrooms, army training, and, of course, video games, to signify what not to do when trying to win at something. But even all these years later, it's still incredibly funny.