1. Kaido
I expected world strongest creature to do what Madara did against 5 kages . Was thinking beating him at the end would require teamwork and combination of attacks from Luffy , Zoro , Law , Sanji and so , didnt expect G5 Luffy would do it alone in the end.
Being effectively stalled by Yamato ( a YC level character ) , and needing help to defeat Oden ( Whitebeard underling ) also ruined all hype about him.
Later Kizaru outperforming G4 Luffy Snakeman is such casual way put final nail in the coffin for this character fraudulent hype.
Also as character he just sucks .
2. Kid
Getting one shot against Shanks. Enough said.
3. Smoker
Had high hopes for this guy , but he turned out to be quite a fodder.