Now that I'm into season 14 of my rewatch (only up through episode 6 so far), I think I have a definitive list of the characters I hated the most. I'm eliminating minor characters/guest stars. This does not include characters I loved to hate, like Abby or Joshua or Jill, but the ones that I believe truly did not contribute well to the show.
Kenny and Ginger (why? There was nothing there. Ever.)
Diana (The most annoyingly selfish teenager ever.)
Ciji/Cathy (though I did like to hate Chip and Joshua, so I realize these were necessary characters)
Olivia (The second most annoyingly selfish teenager ever.)
Johnny Roark (that accent--'nuff said)
Linda Fairgate (how many times was she retconned? 10?)
Aunt Ginny (hard to like Jason's psycho mother)
Danny and Amanda (Why? Why? Why?)
Kate (the most boring character to ever go through multiple angst sessions)
Boring Oceanographer
Alex (another pointless character retconned and then dropped)
Pierce and the redhead from his past (I like him as Captain Pike, but not Pierce--never Pierce) and the redhead was just stupidly inconsistent
And the winner for the worst character on the show: Due to bad writing, bad acting, bad accent, bad concept, bad backstory, inconsistent characterization, and all around vomit-inducing:
Vanessa Hunt