The only one that really sticks with me was this one time in Fallout 3.
I'd picked up Shorty, Red, and Sticky and was escorting them to Bigtown. (since I hadn't been there yet) Along the way we ran across some Super Mutants, so I broke out Vengeance and fired up VATS to try and deal with one.
The instant I start firing, Shorty jumped in front of my gun, and STOOD THERE while I helplessly (since you can't interrupt a VATS sequence once it's begun) filled him full of charged particles. Yes, you read that right, he stood in front of me and tried to catch lasers with his face until he died.
Ten seconds later I'm 50 ECPs down, Shorty is dead, and I've managed to score absolutely zero hits on the super mutant who was charging up with intent to feed me my own legs because that DIPSHIT had made me waste every single shot on him. And Red had the cheek to screech about Shorty being a pile of leaky meat. That is not tragic, you hopelessly retarded bint, that's culling the bloody stupid!
So I ragequit and decided to fire up some Quake 4 where at least the friendly NPCs could outsmart an amoeba and didn't jump in front of my gun and whine at me when I shoot the stupid berks.