I really don't like what I call "bully couples" where the guy is downright mean, and the girl just takes it. There are two examples of this in the K dramas I've watched.
The first is Geum Jan Di and Gu Jun Pyo from Boys Over Flowers
I had issues with this couple because Gu Jun Pyo was a bully, and when he finally liked Geum Jan Di, he still let her get pushed around and insulted by his mother. Not only that, he acted aloof, almost married someone else and literally forgot her. I lost count of all the things that Geum Jan Di put up with, but it irritated me that she waited and waited and waited while Gu Jun Pyo did whatever he wanted. It seemed like Gu Jun Pyo was too selfish while Geum Jan Di was too selfless.
The second example is Baek Seung Jo and Oh Ha Ni.
Oh Ha Ni was literally obsessed with Baek Seung Jo and that bothered me, but what really bothered me was the way he treated her. Baek Seung Jo was downright mean and rude. He graded her love letter, ostracized her, treated her like she was stupid, constantly put her down and of course the classic, messed around with her feelings. He would be nice one moment and cruel the next. He would tell her one thing and then act completely different. The one other thing that irritated me about this couple was that Oh Ha Ni only wanted to marry Baek Seung Jo. That's it. She had no other goals or dreams, and it took a long time (more than half the show) for that to change.