Actors I didn't like

For Blood (main), and You're All Surrounded (main). Very bland actor, with a mask as a face: no expression whatsoever and line delivery monotonous. I am avoiding him actively.

For Pinocchio (main). The lack of dynamism was obvious, he didn't look or sound natural. I was rooting for his rival! To think he's one of the popular actors, I am dumbfounded. I have even watched some bits of other shows he's done:  I can confirm I am avoiding him. He's not a terrible actor per se, but he's way too dull on screen to be interesting.

For She was Pretty. I'm not sure why I didn't click with her. She was supposed to be friendly, happy, warm...but it did not ring true. She was too much maybe. Too happy, too friendly, too perfect, when she was supposed to be imperfect.
And now in Kill me, Heal me. Her acting is so forced, she's very close to cringy. I am avoiding her.

For Beautiful Gong Shim (support). He played the villain in the OTT way reserved for children's shows.  Same OTT style in What's wrong with secretary Kim (support). Forced acting and painful to watch.

For A Korean Odyssey (main). Her facial expressions are so wooden! Her line delivery isn't too bad, but her face does not move, so I found it hard to love her. Has she had too much surgery, a-la-Nicole Kidman?? Tried her in another drama. She's still a mask.  An actress I am avoiding now.

For You are Beautiful (main), and to some extent, Pinocchio (main). In the former, she was extremely irritating and OTT-cutesy. In the latter, she didn't convince me and I never managed to warm up to her. HOWEVER, I watched 2 of her recent movies since, and her acting has improved tremendously. So I am not avoiding her anymore, only her old stuff.

For Blood (main). This actress lacks subtlety in her acting, and I might be cruel saying this, but her squeaky voice grates me.

For My Country (main), the Light in your Eyes (support), and many more. This actor plays the same character over and over: quiet, sullen and aloof. He is expressionless and emotionless. Whenever I see him, my heart sinks.

For What's wrong with Secretary Kim (support), Bring it on Ghost (support) and I'm not a Robot(support). Not a terrible actor per se, but far from being great or even fine. He has done enough dramas by now to have experience, and yet, I never believe in his character. Just like all of the other actors on this list, he lacks subtlety.

For Sweet Stranger and Me (support).  Another OTT actress better suited to children's shows. Hopefully she'll gain experience as she grows up, because she was hard to watch.

For You are beautiful (main). OTT, so OTT,  acts like a real life manga character, with expressions straight from cartoon land. Line delivery ok.

For Thirty but Seventeen (support) and Moon Lovers (support). Very unconvincing. Not exactly wooden, but very monotonous line delivery and no feelings on show. 

In Masters' Sun (main) and in Kill me, Heal Me (support). She seems more interested in keeping a flawless appearance on screen than expressing true emotions. Everything looks calculated, from her poses to her slow movements, to her air hostess voice, as if each scene was a photograph for a magazine. She needs to loosen up.

She was okay (read: average) in Rooftop Prince, but so unbearable in The Light in your Eyes that I had to drop the series in spite of enjoying the plot so far. She grated on my nerves too badly to carry on.

In Children of Nobody (main). Her acting was that of a zombie: no dynamism, monotone line delivery, emotions flatly shown. She looked bored or just awake and in need of a coffee. 

She's played in dramas/movies I've loved, and I didn't hate any of the characters she's played. So why is she here? Because she never managed to make me LOVE her characters. She acts as the same fragile, sensitive girl next door over and over, and she looks bored on screen because of her monotonous line delivery. So not awful to the point of me avoiding her, just...can do better.

For My Only Love Song (main). Want to see how NOT to act? Watch him and his caricature of a baddie. I hope he was asked to play in this atrocious, flamboyant way and that he's normally a more subtle actor, but in this, I could not stand to watch any of his scenes. He ruined the mood every time. Edit: I guess he was asked to, as he is good in The Guardians (support) and Gu Family book (support). So he's a one bad job actor. I forgive him.

In Guardian (main). Apparently a successful actor, that others praised in Guardian. However I found him apathetic and his few expressions didn't look genuine. He was supposed to play a serious character, but he did not achieve to make him look realistic or even engaging. Serious doesn't mean only the cliche no smile/lack of reaction. His body was too stiff, his eyes dead. He lacked that little oomph other actors have. I'm willing to give him another chance though, as maybe this character just didn't suit him.

In Beyond Evil(support). She showed the same problem as all my other disliked actors: she exaggerated too much her behaviour, expressions and voice. Compared to the natural acting of her co-stars, she sounded like a bad rookie.