AI companions
Crucible mission, I gotta push an intersection that's got master and legend monolith on three sides, and it's still easier to do by myself than to let those three morons help.
Most of the time they just push me out of cover, or walk in front of my burst, dying instantly, if I let them push and hang back, it takes 'em a good minute of sustained fire to take down a single enemy, they are invincible (except friendly fire) and still worse that useless.
I loathe them.