Day 4: First dragon your character slew (or some other powerful monster).
During my early years with D&D we never had any consistent world development or continuity between adventures. We'd make new characters for each adventure; if we did play the same character in another adventure it was seldom. Either way, we never advanced beyond the starting levels. Thus we never encountered the iconic "powerful monsters"; we never got high enough to stand a chance against them.
Because of these reasons it was many years after my introduction that I killed my first dragon. We were playing D&D at the local university. It was a huge group of about 16 players. The DM was also running a loose game where you could play a variety of alternate races and classes (we had vampire and githyanki characters). I had rolled absolutely pathetic on my stat rolls (nothing over a 12 and an INT of 4). I ended up making a druid but was often fairly useless in the party, or at the least, highly overshadowed. However, the rest of the party (and I suspect the DM) took pity on me. At one point we found a magical acorn in a treasure trove and since I was the druid they gave it to me. It had one shot of a petrification attack.
I held onto that acorn for many adventures. One night we ended up fighting a huge dragon that was causing a lot of damage to the party. We kept hitting it with everything we had but it wasn't going down. After one of its breath attacks, my character jumped into its mouth and hit it with the magic acorn. I had jumped into the mouth because I didn't want to miss with a throw. The dragon failed its save and was instantly turned to stone.
I got to be the hero that night.