Like poor old Sebastian and Jacob Taylor. While they don't do anything that makes them hateworthy, the size of their threads on these forums make it rather obvious that not many people find them particularly interesting, compared to the other companions. They suffer from the worst fate that can befall a character, short of being seen as The Scrappy, the fans simply found them dull.
Which makes me wonder why people are so content to throw hate at Cullen, who people actually like to talk about? Isn't the fact that we're paying attention actually showing that he's a character we want to know more about and see more of?
Well, there was that one moment where Sebastian threatened to take an entire city state to war, which would cause many more deaths than the destruction of one building, over one man who wasn't even from that city state. 
I don't hate Sebastian but he has made me facepalm and desire a murder knife option.
Jacob I don't hate, but he didn't really attract me, either, and his 180 in personality once aboard the Normandy was weird to me. It was like he and Miranda switched personalities once on the Normandy. Jacob became closed off and private, while Miranda because open and happy to talk about herself and the organisation she worked for.
I can understand why those who romanced him would be less than pleased with that guy, though...