Hold your fire! Friendlies coming thr-, oh you shot at them already, good job idiot

I generally don't mind friendly fire. However, that's only the case if friendlies are actually doing something, instead of just simply getting in your way.

Case in point, in Halo for example, you can accidentally shoot the marines, but as long as you only do it now and then, they don't care (it's annoying when they hit you though on accident). But if you do it too much, then they turn on you (it's fun killing captain keyes in the beginning, although the marines that show up are invincible and can't be killed, which kind of sucks lol). The robot guys will do that too in that one stage where they're friendly. Was playing with a friend one time, and he kept shooting at them just to see what happened. Well, they turned on us, and although they continued to fight the zerg, er I mean flood, they attacked us throughout the rest of the level as well.

However, as mentioned earlier, I hate it in arcade shooters, esp. House of the Dead and Area 51. Although House of the Dead is at least sort of cool in that people you save will usually either give you an item or perhaps a shortcut through the stage, in Area 51 they're just there to make you lose life if you shoot them (cause although they're shooting, they never actually hit anything). I know they're just there to penalize you for doing something you shouldn't do, but sometimes they get in the way so badly that you will probably either hit them, or get hit by a bad guy in the process.

Jam it back in, in the dark.