I had a GM that ruled that someone shooting me as an Untouchable during combat was valid because the people were taking our weapons and I reasoned it was a bad idea to let them take them, because lore is that Untouchables are apparently slaves or something and don't do anything autonomously. I reasoned my way to a conclusion and pretty much everyone but the player that shot me was on my side, and the GM was adamant that lore made it all ok to teamkill me over self-defense, basically. Does it help that the party was trying to reason with heretics while I sat there and watched until they came at me?

PvP is always rough.

But you do realize that an Untouchable is the creepy relative that no-one likes in WH40K terms. Everyone not only psykers find you uncomfortable to be around. That will make you a target for random violence pretty regularly.

I understood I would be shunned and whatnot, but I didn't think because I attempted to PLAY MY GODDAMN CHARACTER I was open to being shot with no ooc recourse. That's the part I'm calling bull on. My character analyzed the fact that without weapons, there was no way to fight out of a 40+ enemy ambush should they choose to attack us, and so I decided we shouldn't drop our weapons, but there's no way to communicate with the team while the people are right there taking our ****, so I just opened fire and the GM basically said I had no room to complain about teamkilling which, when I GM, I never allow without serious consequences in-game. Even if its an outcast-type character, you've betrayed one of your comrades who trusted you, and word spreads of that, giving you penalties on anything involving a character that isn't a hostile faction, because nobody wants to trust you.

So the party was trying to reason with the 40+ armed Heretics surrounding your group when you pulled up your weapon(s) and attempted to shoot it out with them (Heretics) and 1 member of your party shot you down. Did the rest of the party, join in the attempted shoot out attempt, or just kinda looked shocked, when the you pulled up gun(s)? And what was the negotiation status when you pulled gun(s)?

Did you team not have Cipher and/or Secret Language - Acolyte? That would given you a way to have communicated your plan.

If the remaining party members OOC agree with you, then I wonder if IC if they will have trouble trusting the 1 who gunned down a teammate.