Most of my notable memories are from competitive successes in online leagues. I still remember one FFA tournament in Halo:CE (10 people per group, 50% health snipers, first to 25 kills advances; after group stages, it's just seeded 1v1's), I was in a group with a player from one of the top 2 ranked teams in the league. Everyone expected him to win that group, and whataya know, I squeaked ahead somehow and won lol.
Next round, I was seeded against literally the #1 player in the entire league, and I immediately started receiving so much shit talk like "Haha, you should've just forfeited that group, now you're gonna get raped 1v1". I remember being pretty nervous and spooked too, but I performed pretty well. Started strong leading at most 7-4, and then losing something like 15-11. It was a pretty fair and close fight.
Later down the line, I received an invite to join that #1 player's team (the other #1/#2 ranked team in the league; it constantly went back and forth). The first tournament I played with them, I was on starting roster, and we won. That was a super ultra rush, and also the point where I started receiving a ton of respect as one of the top players. Even the league coordinator admitted I was deserving of my starting position.
Another fond memory I have is of the first match I received a 24-hr ban for "suspected hacking". I performed too well that they thought it wasn't real lol. In the time before anticheats, the way they "checked" hacks was you were supposed to record your POV via fraps, but my computer was so shit that I couldn't both play and fraps unless I dropped below 30 fps. So at the end of the match they told me to upload my fraps, I said I didn't have it, and I got banned :D. I remember feeling super proud that I was so good they thought I was a machine, and also happy because I had two friends sitting on my bed in my room watching "My Super Sweet 16" and waiting for me to finish playing so we could hang out haha.
God I could ramble about these sorta things for ages. It's just such a rush. I miss playing competitive!