The Girl Who Sees Scents
Warm and Cozy

simply, all the drama that cast Shin Se Kyung and Kang So Ra it in, i dont watch it.
Itazura na Kiss (and all related titles), Rich Man Poor Woman, etc. -- I'll pass on dramas featuring relationships where one person is cold/manipulative/dismissive/cruel toward the other person, whilst the other person goes along with it or eventually gets worn down by it and calls it love (even more negative points if supporting characters keep telling that person how romantic the treatment is). Lived it; don't want to watch it.

Boku no Ita Jikan -- I have no doubt that Miura Haruma is amazing in this (dude has enough talent for ten actors) and it's supposed to be incredible, but I just can't handle it.
Cheese in the Trap, even if im a fan of the genre, im definetly with no mood for shitty endings
Descendants of the sun , jesus christ i've heard so many time of it that i'm already sick of it!
 And i saw kill me ,heal me and it were...BORINNNNNNGGGGG!!!!
Hahahaha me too @yoona! I haven't watched descendants of the sun, and I dropped Doctors... I just can't watch it. I don't know why....
descendants of the sun
I refuse to watch all the dramas where UEE has a main role or even supporting role (like in You're are beautiful I had to drop the drama because of her). I just can't with her. She is such a bad actress I see zero emotion in her eyes when she acts. And I also CANNOT watch Secret Garden no matter what people say or what I read I just can't. I find all the actors really ugly and the quality is ewwww. 
Not really something specific, but any soap I refuse to watch (150 episodes or more)
Yong-Pal, Descendants of the sun, Doctors...I've tried, but aren't my thing
Descendants of the Sun
Kill Me, Heal Me
You Who Came from the Stars
Healer
The Master's Sun
It's Okay, That's Love
Another Miss Oh
The Heirs or any lee min ho dramas
You who came from the stars

I didn't want to watch Kill me, heal me or the master's sun but I endend up loving them!!!!

Any drama where the male lead is younger than the female lead.

Kimi wa petto
My lovely Kim san soo
Flower Boy Ramyun Shop
Sappuri