If someone gives you a funny look, and isn't carrying a weapon (Or is holding a spy weapon), but appears to be on your team, then I usually just reflex, and shoot them. At my server, friendly fire isn't on, so if it's a spy, they die. If not, they're on my side, and I stop shooting. Simple logic. But some people don't get it, so they keep shooting them, and the other team notices' that they have an "invincible" teammate. Basic logic... they shoot you, causing you to die, and shout curses at your teammate.
