I've played Halo for a fairly long time now. Beaten the campaigns on legendary (even Halo 2,) and got myself a nice collection of medals in multiplayer. Kilimanjaro, Inconceivable, Perfection, and so on. But none of that compares to a certain session of 1v1 matches I had years ago where I came out victorious.
I was introduced to the series by a friend of mine, named Tyler. We played Halo 2 together as kids. Even though I enjoyed it a lot, Tyler was way better than me. He insisted on playing PVP, probably because we'd win every time. But one day, while I was looking for help with the campaign, I learned about the Plasma Pistol's EMP + headshot combo. During our next 1v1, I used a Plasma Pistol and a BR against Tyler, and I totally smoked him.
The cherry on top of all this is that one of these matches took place on Terminal. There was one point where he was chasing me, but before he could get his last shot off, he stepped onto the tracks and got obliterated by the train. He flipped his -Yoink- and I couldn't stop laughing.
I've also got a close second. One time In Halo 4, in a BTB match on meltdown, the enemy team controlled both of the Mantis mechs. I managed to sneak up and blow both of them up, one right after the other. I think I still have the clip saved on my old 360, I'll have to look for it sometime.