The first one that comes to mind is the escort mission in Spartan: Total Warrior where you have to escort Archimedes (I think; it's been a few years since I've played it.) Granted, most escort missions are bad, but this was a special kind of bad. He'd run in front of you, try to hide in the throng of people trying to kill him, and generally be a complete idiot. I doubt I would've passed it had I not been playing on easy.