I always find it amusing when a newbie teammate is shooting at me in the dark, and because of my quicker reflexes and sharper aim I manage to kill him first.
It's a big problem when a teammate makes the first shot and you don't have time to stare through a dark room to identify him, which is only part of why I try to give slack.
But you know, there are tactics you can use to make yourself seem less threatening to your team, like exposing MORE of your body, and looking at them (acknowledging that you know they're there) but not acting upon it. However, raising your sights is a death sentence.
I do take note of times when I make the first shot, miss, yet a teammate doesn't shoot back, or when a teammate doesn't shoot at me despite me behaving ambiguously or threateningly. I appreciate those moments.