Rules are fun (unless they're used against me!)

So before my dear friend became a confused DM he was a cleric in a game of D&D we had with Mike, James and Son (also from one of mine previous tales). I'm gonna call him Paul from now on.

We began this tale on AD&D and then moved forward to D&D3E, the were about level 18 when the transition happened, so we got into the Epic Level handbook pretty soon and we kept going 'till level 27. We used a national setting, called Tormenta, but I've made some changes to include a few classic D&D elements, like the Hand of Vecna, and everything was very casual and fun. The party consisted on James as an Undead Fighter/Mage, Mike as a Winged Monk (with a dragon mate), Son as a Half-Celestial Paladin, Paul as a I-Can't-Remember Cleric and AJ as our Fiendish Warrior. The reason they all have kits is because they were so weak that when we transitioned to D&D3E the characters were so weak I had to do something, so I custom made some kits and gave them as "rewards" to elevate the party power level. It worked VERY WELL! To this day I'm a little proud of how balanced things ended up, and everyone was happy with the new flavors of their characters.

The campaign had been going for almost two and a half years, so I felt it was time to end the adventures of that group. The group originally had more players and their characters were kept as tribute, also they had the personalities and traits of the old players, so it was real fun to have our friends in game in that way. One of them was a wizard that I made into a god in disguise, and he killed the BBEG of the campaign, revealed himself to be a deity and asked for the players help to kill Tiamat (every single player in the group always wanted to face Tiamat, so I gave them this parting gift).

The plan would be for them to open a portal to the realm where Tiamat was, the wizard would step in and sacrifice himself and his godlike status to make Tiamat mortal, and the party would finish her off.

They went on to the battle, and everything was according to plan, except our Fighter wasn't hitting as much as he liked. He started to sulk as his damage wasn't astronomical and the other players, namely the monk and the cleric, were also hitting hard and surpassing his damage. So he got fed up ant throwed a tantrum that literally ended the game right there. We packed our stuff and left and we never got to see the end of that battle. Everyone got super disapointed, and every once in a while they kept bringing it up with me like "Hey, how about we get back into that Tiamat battle? Just to finish it?" and I always refused, it was too bitter memory for me to relive.

But everyone wanted something more, to make almost three years of game amount to something, so I made a deal with them. We would leave the old campaign alone, but they could create character sheets for their sons/daughters and we would start something new based on what happened. They all agreed, even AJ (whose motto was "You all know how I am, it's your choice to still hang out with me.") and they proceed to make characters based on their old heroes that vanished bravely while stoping Tiamat to invade their realm (yeah, it got canon that mid fight they all vanished and my plan would be for it to become the climax of this new game).

They started low, but with some power and a lot of money so I made a few adjustments to the first adventure, but also was prepared to change everything on the go since it was new territory for me. AJ used his money to buy full plate armor, and everyone got well equipped too, and before we started we made some adjustments to the House rules.

We had a rule that stated that every nat 20 was automatic success and every nat 1 was automatic fail. This led to a comical 1-hit-kill on a shadow dragon when Paul got cornered by one. Also we were introducing the instant kills, if you rolled a 20 when confirming your critical you would kill the target on spot. Both rules applied to players as well as monsters, and everyone cheered at the chance of killing a dragon with one lucky hit.

The adventure started with the heirs going to investigate a crypt that was spewing undead on a nearby town, it was supposed to be a really easy adventure until the final boss came around. I wanted to give them all the sense of power, to just power trough some low level zombies and stuff. Well...

They got down into the crypt and the first room is filled with skelletons, so they all laugh, as i expected, and start to beat the poor piles of bones. Then the monsters turn comes, and I flail their bony hands at the overpowered players until one lucky skelleton just manages to roll a nat20 against AJ. We all start laughing, since he was the first to be hit, but when I go to confirm the critical hit I roll another 20. Before I could say anything AJ, again, flips out in rage. Yelling how it was cheat (I was rolling the dice in front of them), how it was impossible for a skelleton to kill him with armor (but the "armor" thing never stoped him to hit golems made of metal before), how I didn't want him to play from the beginning (even if I was the one who invited him back), how I was making up the rules (the rules we all had agreed not 30min before) and he refused to die. Everyone just packed their stuff and we all left and never again talked about "that old campaign" also never invited AJ to play with us again.

It serves me right to try and play with someone that used to say the Vampire: the Masquerade wasn't RPG because it wasn't medieval fantasy...

EDIT: People are telling me I've been unfair with the insta-kill rule so I'd like to explain it a little better. The first thing to remember is that the game was a "sequel" to an almost three year campaign, so the players already had a clue about what worked and what not for them. They agreed on the first ruling of nat1/nat20 because they wanted to have at least 5% chance to accomplish something, even if that gave them a 5% chance of fail every time. The 20/20-hit-kill rule was agreed upon because they were just too powerful, it was unanimous the thought that we had to rise the stakes so they'd feel threatened, otherwise it would be a walk on the park. Never I did impose anything on them, and it was all agreed by EVERYONE and, of course, it was always open to change anytime someone had a problem (and had the maturity to discuss as a normal person). The most important thing about the game was to have fun, and have fun together.