5. The Forces
The Forces might technically be four different characters but we're grouping them together here for a reason. One wasn't particularly more annoying than the others; they just all became such a thorn in fans' sides that it was hard for them to enjoy anything that The Forces did. Honestly, they are justified in feeling that way.
The Sage, Strength, and Still Forces all emerged with their own avatars, joining the Speed Force, Nora, in becoming allies for Team Flash. But it wasn't all good, for the Forces had their own agenda and eventually turned on Barry Allen and Iris West, who they believed were their "parents" (even though one of the Forces took on the form of Barry Allen's mother).
The Forces got far too much focus, once again resulting in too many characters for The Flash to balance. They also added nothing of value to it. Speed Force Nora was always a beloved part of the show, but whatever it was they were trying to accomplish with her heel turn here did not pay off. Nobody ever really understood why The Forces started acting up, but in case you thought the show learned its lesson from the lacklustre storyline, it only went and brought in inherently evil versions of them known as the Negative Forces.
Honestly, what was happening in season 7?