I hate Nick Valentine... I'm shooting at Super Mutants from inside a bathroom. Nick Valentine decides to run INTO the bathroom just as a Supermutant throws a grenade, preventing me from dodging said grenade. Also, not quite as deadly, but I'll be firing my combat shotgun at vermin, and Nick all too frequently decides to jump in front of my gunshots in order to pistol-whip said vermin, taking the full brunt of my shotgun blast.
I'm in a radioactive hotspot, and my companion decides right at that moment that it's a good time to talk about our feelings... By the time I untangle myself from the conversation, half my health bar is red. I've had the same thing happen just as a big battle is about to descend upon us. I've bled to death while some idiot companion decides that he needs to get something off his chest at that very moment. You have a small window to extricate yourself, but after that, it's all automated, and the worse the sounds of combat (or radiation) gets, the more it seems like the whole thing is taking place in slow motion.