My actual first experience was pretty much just rolling dice to see how it worked.

My second time, which I consider my first real game, I was playing a first level paladin in OD&D with only the first supplement Greyhawk. The party ranged from 1st to 5th level, was entirely Lawful (which meant Good).

My paladin couldn't afford a sword, and was wielding a mace.

After several encounters, a couple levels down in the dungeon, we were all down to 3 or fewer hit points. (Remember, in this game, 0 hit points is dead.) My paladin had a single hit point left.

The treasure we had just found included a sword, which the paladin asked for. He received the right to pick it up. Unfortunately, it was a high-ego chaotic sword, and the first thing that should happen when my paladin touched it is that he should have received 2d6 points of damage, which would have killed the character. The DM made a few rolls behind the screen, and then wrote and handed me a note.

"This Chaotic sword has changed your alignment. You are now chaotic, and holding a chaotic Flaming Sword."

I thought for a moment, and asked to speak to him privately. When we got into the other room, I told him, "I don't have any questions for you. I just want them to believe you gave me more information than the note had." I told him my plan, we waited a couple more minutes, and then we walked back in.

My (ex-)paladin told the group, "This is a Holy Sword with a quest I have to take on alone. I need you to go back the way you came. It's important that you do as I ask. Go back single file, and no matter what you hear, DON'T LOOK BACK."

Of course the five characters trusted my paladin, and did as he asked. My chaotic ex-paladin came up and stabbed each one in the back. Several times the DM said, "You hear a stab behind you, and a body slumping." "We don't look back." After five times, he told them that they were all dead.

So in my first game of D&D, my paladin murdered an entire lawful party.