So, I've been playing DnD for a long time. One adventure, we had switched to Advancement Points, meaning we gained more from role play than combat. So we built a party based around social ideas rather than combat builds.
I am playing a pacifist Sorceror who literally has always goes out of his way to avoid a fight, along with a Trickery Cleric who was a benign prankster and a ranger who just wanted to be a chef.
The party was fun, and we all seemed to have fun trying to create non violent ways of beating quests. Then the "Lawful Good" Murder Paladin joined.
A Dragonborn Devotion Paladin of Bahamut, he and my character immediately did not get along. (my guy's backstory was that he was a brass dragon Wished into human form who was adventuring to become a dragon again. MP accused him of lying and offending dragons with that tale, as this Paladin was obsessed with draconic glory)
We came across a goblin village. My guy speaks Goblin, so obviously I went to talk. I'm met with paranoia but the goblins end up being friendly enough. Then… MP…
MP insists I translate as he grabs adult goblins and burns them alive with his breath weapon. He grabs the children and threatens them to "serve Bahamut or suffer the same." I argue, yelling for the goblins to run away.
My party went with the paladin's plan and started gathering the children. I argue but everyone turned on me fast. "they're just goblins, it's not like they're human" To my guy, these are just children and he refuses to aid the party. Someone cast Tongues and now the Paladin can threaten the children.
The children agree, if he'll spare their lives. Once they sobbingly agree, he brands them and chains them up. I argue "how can you be Lawful Good and do this?"
MP: "They are evil creatures. I'm giving them a chance to serve my god for the betterment of their lives. They'll be grateful."
I wanted to start PVP, but MP had an insane AC due to some magic items and stat building and my Sorceror is not built for combat. And the rest of the party was now laughing at this debacle, for my Sorceror fought pretty pathetic compared to him. My character left the party.
Next session I brought in my Lawful Evil Yuan Ti, who burned all the children to death "by accident" when MP was going to sell the children to slavers to get coin for his church. To be fair I killed the slavers too.
We journeyed on and my guy found numerous ways to subtly ruin all of MP's plans. My Yuan-Ti had an Int over 20, while MP had dumped Int in favor of building entirely for AC. Thus the player knew I was a saboteur but the character remained clueless, especially since the party thought it was funny.
My BF joined the party soon after and MP left the table, as my BF has a reputation for being a strategist and thus always gets forced into being party leader. The campaign died soon after, as the party quickly beat the adventure once he was leading us.
It all ended with MP and I, who are friends in real life, deciding amicably not play at the same table again. However, he did join a table where I was DMing, which is a whole other story.