Terrible AI Teammates in Video Games

In video games where players are part of a team, the AI needs to be competent. What good are your computer controlled teammates if all they do is hinder rather then help? In many video games, the AI is so bad they seem like the developers' afterthought. Here's some terrible video game AI that I've seen.

Left 4 Dead
Good luck trying to play either of the Left 4 Dead games without at least one other human. The AI seem determined to make your life during the zombie apocalypse as difficult as possible. The sad thing is in most cases, they're just trying to help. There's always plenty of zombies for the four you to deal with, but one of the AI always jumps in front of your shot and you shoot them instead. Also, they pick the worst times to heal you. When you're about to be attacked isn't the best time to be handed pills.

Halo
The friendly AI in the Halo games are pretty bad. Don't let them drive unless you want to careen off a cliff and don't expect them to actually kill any enemies they shoot. They also don't seem to understand the term "friendly fire", because they will shoot and manage to kill you. If only they were so good at killing who they were suppose to in the first place.

Star Wars Battlefront 1 and 2
Don't expect these troopers to actually hit anything at all. I think they're just there for show. It looks cool that you have 50 Stormtroopers as teammates, but it's a bit tiring when you realize you're doing all work. On any map, whether it's instant action or campaign, the AI does not help. You're left searching the battlefield for that last enemy, while they're running around looking idiotic.

Mass Effect
Your AI teammates in Mass Effect like to jump in the way during fights, a lot. They don't move or obey you when told. They like to waste ammo by trying to shoot through walls and other solid objects. Your team will attack any enemy even if they don't have a clear line of fire. At least Bioware revamped the AI in Mass Effect 2.

Resident Evil 5
Playing Resident Evil 5 in single player is an exercise in patience. Your sidekick, Sheva, frequently likes to waste all the bullets by shooting at walls. Give her the generade launcher for a tough fight and she'll use the shock baton instead. Unlike the other Resident Evil games, Sheva is a constant companion. The only way to make her useful is to have another person play with you.

Army of Two
You know the AI is going to be terrible when during the training missions at the beginning of the game, your teammate runs around in circles instead of sneaking behind the enemy. If you're not constantly commanding him on what to do, he'll probably do nothing. This opens your teammate up to running around aimlessly and getting shot. Army of Two is best when played with another actual person.

While these bad AI teammates don't necessarily break the game, they are frustrating. It's difficult to play a problem free campaign when you're worried about the AI wasting ammo or running around. In most cases, they seem to want to help, but they hurt the mission instead.