Dan/Blair - I loved them as friends but it just became so forced. That the buildup kind of all went to hell.
Daniel/Emily - I thought they were okay in the beginning. But then Daniel became a total Grayson and it's pretty obvious Emily doesn't care for him at all.
Emily/Jack - I hate forced pairings. They knew each other when they were kids, that's great but it doesn't mean they are meant to be. Also the flashback in S2 to their 'wedding' creeped me out. Jack looked so much older than Emily/Amanda.
Klaus/Caroline - He's attempted to kill her friends more than once and the 'he's a vampire' excuse just doesn't cut it with me. Awful.