I drop so many dramas after only watching one episode, I don't even put most of them on my list. The last one I can remember dropping after watching a considerable amount of episodes: Doctors. I was so excited for Shin Hye's return, but this one just got progressively more disappointing as the episodes went on. Plot was weak and her character could have been so much better. 
Boys over flowers and orange marmalade. It became boring
It's Okay, That's Love [7/16]
-Jealousy Incarnate, I just couldn't get into the humour nor story no matter how hard I tried :(
Uhmmm.. Bridal Mask. Dont know.. I just got bored after episode 1.. 
Drinking Solo/Let's Drink - they took the cold man trope too far and I thought ALL of the characters were awful humans
Imaginary Cat - I usually give dramas four episodes to settle in, I didn't even make it to half way through episode one and I was bored to tears.
On The Way To The Airport. idk i'm just not feeling the story
Woman with a Suitcase 9/16
Local Hero 12/16 - it started ok but then it got more and more boring.