I hated when:
Tomlin & Whitesell wrote John as such a complete dunderhead as to cook up a scheme to sleep with Kristen to prove to Brady that she's a manipulative, lying (etc) witch while Marlena was chalked up to collateral damage.
The entire Princess Gina/JT storyline. Uch. From submarine sex to the reveal & ultimately Hope & Bo losing custody to the Reibers, it just SUCKED.
Anything & everything Alex North.
Anything & everything EJ/Sami.
Sami left Salem and she and John didn't even get a good-bye scene or any flashbacks (I'm REALLY hoping the new writers will give Ali Sweeney (Sami) and Drake Hogestyn (John) some good/happy screen time). Her exit was one of the worst EVER - just really poorly planned out, in my opinion.
Anything & everything with Chris Kositchek pretending to be Roman Brady. The REAL Roman Brady is being held captive on a ranch in California by Lucy Coe and being made to bail hay, feed cattle and drive an old, beat-up truck.
NOTE: Lucy Coe is a character from General Hospital, played by actress Lynn Herring, who is married to Wayne Northrop (original Roman) - JS