Just today, on a 2fort server, I was a medic, following a pyro to the blue team's base, and apparently they had planted a turret near their intelligence. So I was constantly healing him while he moved back and forth to try and destroy it, when another pyro from our team comes by and gets ready to start doing the same thing. Just before he does, I realize that he has very low health, so I start healing him in stead. Before I can tell what's going on, the other Pyro spy checks him, (as it turns out, he actually was a spy) and he shoots both of us in a fraction of a second.