@Stu mentioned two things from our college days which still stridently ring in my ears:
Killing Stevie’s psychopathic, delusional, paranoid magic user in GURPS (yeah!) with Bill, and the nature of betrayal during Diplomacy.
I still appreciate that you did not attempt to dissuade us from our decided course of action. As I recall, we even set up the situation by standing and showing how we were positioned around the magic user, so that there would be a very clear picture of how things were going on. As I recall, though there was a substantial of surprise, Stevie didn’t appear to be angry, brought a new character — one substantially less likely to appear an enemy of the party.
As for Diplomacy, and how it relates to meta-gaming trust, the larger problem is having the goddamned rules explained from the outset. When @vyrrk sat down at the table, the conceit about PvP was sprung on them. It turned out OK, better than OK, sure; but we’ve also heard of transgressive situations when players are robbed of agency or tricked by the GM in a “Whose d20 is bigger?” contest. As for myself, my first Diplomacy game was run by Erik Aldrich, where he said he’d teach us how to play. He neglected to mention that the game centered around backstabbing. So I I spent several hours gaming just to have a big, surprise betrayal by the gentleman who had claimed he’d teach us. This is like learning fencing by receiving a riposte to the heart. I didn’t play the game again for another 30 years.
On a related subject, but not provably related cause, I later murdered Erik’s character in Stu’s GURPS game.