I've left four games
1) I moved.
2) Incompatabiity with GM: It was a Call of Cthulu at a gaming club. My character was a Native American Shaman. The GM said that I had a Spirit Guide. During the game (my first time playing CoC), the character goes insane contacting the spirit guide. It turned out that nobody would let this guy run, because he was all about killing characters- I wish somebody had told me.
3) Incompatability with setting and playstyle: It was a 20+ level 2e game and they were basically playing superheroes in the DND world. One guy had Wolverine guys and regeneration. Another guy was kind of like Green Lantern. I forget what the third guy did. I gave it two sessions before quitting, but I would join with them when they played Talisman.
4) Temporarily quit. Incompatability with player and the playstyle at the time: I returned to a group that I started. The new addition since I left was an obnoxious butt kicking, optimizing, powergamer- jerk was appropriate.
The group was playing Rolemaster. I created a Rogue and made a concious decision not to maximize weapon skills and focus on other skills to aid the party. The ass** goes off on how my character was worthless, because he was not maxed out for combat.
After two sessions, I talked to the GM and excused myself. I told him that I wasn't enjoying the game, because of the jerk player and the total focus on dungeons and combat (which I was not told about). I wanted more of a balance between roleplaying and combat (with a possible leaning toward the former). I wanted to go to towns and cities, interact with NPCs, have adventures outside of the dungeon.
To my surprise, the GM wanted to run those things. However, the jerk was a long time friend of his and would complain if there was anything other than combat. Knowing his friend's preference, he had been catering to his friend's style.
I left for six months to a year. Then, my roommate, who was still playing in the game, invited me back. He was starting a new campaign as the other players (except the jerk) were bored and tired of settling for the current playstyle. The current GM also wanted a different playstyle and needed a break. Furthermroe, it turned out everyone was tolerating the jerk, because they lacked enough players and he behaved much different away from the game. If he didn't change his attitude, they were no longer going to invite him.
I came back to give it a try. Sure enough, the one guy complained every moment that we were not in a dungeon or fighting something. He would demand that we hand waive the rp stuff. His character would go on power trips, threatening NPCs, starting fights.
Eventually, we kicked the guy out. My roommate sat him down several time and told him to change his behavior. The change would last a few sessions and then he would revert. The last straw was when he killed an important NPC with whom the rest of the party was trying to build trust by putting themselves in a vulnerable position. The attack resulted in the party splitting into into three factions. One factions attempted with one group trying to save the NPC. The jerk's character, and another party member caught in the middle not knowing whom to help, but eventually protecting the jerk's character. When we failed to protect the NPC (destruction spells are nasty), my faction told the other two characters we would no longer adventure with them and never wanted to see them again and walked off.
The GM told the jerk to leave as people were tired of his attitude and behavior at the table. His character became a reoccuring villain.
