So here are the things that drive us crazy when watching someone else play, and we're sure you've got plenty more to add, so post them in the comments and let your backseat gamer's voice be heard!
Additional contributions: Eric Bratcher, Mike Grimm, Carolyn Gudmundson, Chris Antista
Running around in an FPS with the gun always pointed at the floor
Above: Those puffs of smoke on the concrete dilineate the Trail of Fail
Are we missing something, or do humans have some hidden vital organ in their feet? It's easy to complain about how an FPS is too “twitch” and how they can't hope to compete with some no-life, caffeine-addled teenager when they're trying to go for a headshot by snapping their reticle half a screen up from where they had it sweeping the linoleum. Hint: it's not just about how fast you can aim – the kid that just owned you came around the corner with his reticle already at head-height, meaning he only had to adjust his aim by millimeters to get a bead on your juicy melon.
Never checking their "six"
This also applies to FPSes, but encompasses any action game. They run to the end of a hall that branches in two directions, and they just turn left, horseblinders on, and wonder why they got shot in the back.
Use a medpack!
Above: Note his health in the lower left, accompanied by two syringes that could bring him to full health
Granted, many games use the regenerating health mechanic, but some still cling to the old days when wounds didn't magically heal themselves. Instead, a gunshot magically healed through the application of a bandage. How crazy does it drive you when your buddy is at 10% health, has multiple medpacks, and yet they charge in, oblivious.
DON'T use a medpack!
The reverse of medpack neglect is medpack gluttony. They've got only a sliver of damage, only one medpack, and – gulp – it's gone. Then, of course, a powerful enemy rounds the corner andhoses them.
Nice controlled burst, nice controlled burst, nice controlled – wait, they've got three shots left, all the enemies are dead, and what do they do? Run into the next room.
Above: *Brrappp* *Brrappp* *Brrappp*... click
Running around a room over and over looking for the obvious exit
They've ran in circles for nearly a minute, and yet you can see the door they've missed – it's right between stacks of shelves. It's totally obvious. How come they can't see it? They also ran right past treasure chests/items that are practically screaming “Pick me up!”
Constantly accidentally going back the way they came
Above: "Let's see now... there are a bout fifty potential doors here, but I have the nagging feeling I didn't check the one behind me"
When the visual deficiencies aren't making the game space look like a curtain of camouflage, then the spacial awareness train has left the station – okay, so they ran into the room, and yes, it has two other exits, but does spinning the camera a bit really confuse them so much that they always run back out the entrance, stand there confused, and run back through a third time?
NOT missing anything
Buddha said that the optimal path is one between two opposite extremes. Or wait, was that Keanu Reeves?
Above: Keanu + filthy beard + mysticism + non-English subtitles = WIN
Anyway, the other side of not noticing important objects or doors, is trying to open/search EVERYTHING. It's particularly annoying in games where interactive objects look different from things like doors that are just textures painted on walls. No, that blurry pile of junk isNOT a treasure chest.