The cast of Final Fantasy XIII was truly awful and the only explanation that I can think of for why they sucked so much is that the designers intentionally tried to create the worst bunch of characters ever. Or they were all hit really hard in their heads many times during the development process.
I'm also not surprised to see so many mention Emil from ToS2. I really wanted to strangle that good-for-nothing c*nt.
The VP in Citizens of Earth got many death threats sent to him from my general direction. Not so much because of his character or dialogue (he was actually kinda funny) but because of him interrupting the battles with tedious one-liners the whole damn time. Sure, I get that you won't do any fighting by yourself, and it's fitting that you'll just send everyone else to do the work for you, but for the love of f*ck could you please shut up!?
And, I kinda hate Luigi with a passion. When I played Luigi's Mansion my main thought was "God I hate Luigi", and when I played New Super Luigi U I had very similar thoughts pop up in my mind. He's a spineless, uncontrollable idiot and if my #1 wish is for a game where you get to collect and brutally destroy all copies of Hyper Dimension Neptunia, my #2 would be a game where you get to do all sorts of nasty things to Luigi while he cries to deaf ears.