The first thing I recall killing was...troglodytes.
In the first games that I played in high school (24 or so years ago), the DM had us adventuring in a city...sorta. Apparently the city had been rebuilt many times over the ages, and there were prime dungeons down deep underneath everything. There were doorways/portals/passages, some widely known and others...less known...that would take people brave (or stupid) enough into secret monster lairs. Sometimes the monsters came to the surface and hunted humans in the shadowy places, but I guess that the local PTB couldn't be bothered to do anything about them.
So, a bunch of our characters, including the barbaric Gaelic fighter, played by your humble narrator -- who was armed with a dagger, broadword and morningstar -- would gather together, sneak through a portal and start monsterhunting. Deep under the rancid city sewers, through empty lost rubble-choked streets, tripping over the detritus of past civilizations and squeezing through narrow, fungus-filled corridors, we encountered a reasonably solid-looking door. We listened; din't hear nuthin. The rest of the band starts quietly discussing what our options were.
So I kicks in the door with a hideous Highlander ululation, and sees:
A longish room, with a table at its center; around the table were seated a group of reptile-y things with tall crests on their skulls.
"Troglodytes!" someone hissed (probably the magic-user; he was fairly well-educated).
On the table was a live human, trussed-up on a large platter with a fruit in his mouth.
With a bellow, I starts hacking with me broadsword and smashing with me meat-tenderizer, laying waste to many of the trogs.
Things are a little hazy after that, but what I remember is that I woke up wrapped in bandages made of torn cloaks and the like, in brain-scrambling pain. Between some healing draughts that the rest of the group had found in the trogs' stuff, and natural healing, I survived to loot another lost treasure or 50.
It was...glorious...