Doflamingo and Katakuri come to mind. Not sure if this one counts, but the most egregious one may be the Meme Team. The SHs escaping them at WCI was total bullshit and Oda had to have the plot bend over backwards for them. Meme falling for a fake seaweed haired skeleton, Perospero not shooting the Vinsmokes even after Katakuri told them to do their job, Smoothie and Compote vanishing into thin air, Katakuri not getting the idea to destroy the Sunny until AFTER he was off it, Meme constantly getting humiliated during the Great Cake Chase, the fucking awful copout with the Sunny at the end, etc.