For some apparent reason, this ONLY happens to me in a Call of Duty title. My first controller was all over the place. I was throwing flashbangs and swapping weapons when I didn't even press the button for doing so. Eventually it got to the point where I was aiming down the sights and couldn't come back out of it.
Eventually I had enough and bought another controller. I've only had it for a couple months and now we're back to throwing flashbangs and swapping weapons when I didn't ask the game to. And I handle my controllers carefully. What is going on, and why does this happen? How many more controllers am I going to go through before I find one that doesn't screw up?
Another possibility is what happened to a controller of mine. I have horrible static electricity problems in my house. If it is dry, I can't walk 2 feet without building up an unpleasant amount of static. One time I went over to grab a controller which was plugged into the console charging, and POP. Controller was fried. It partially worked, but it did wierd stuff and wasn't playable. Maybe you shocked both controllers.