The thing that irritates me the most is "teasing" something so much that we end up not caring at all about it, where it loses its value by the time he pays it off.... I'll give you few examples:
1- Oden and Kawamatsu Sihlouette being in constant tease for a lot of times, to a point it became annoying and ruining some scenes because a scene looks drawn in normal way for two pages or more while only Oden in sihlouette... I find sihlouette only used in good way if someone was talking about an absent person not present in the moment... but showing a complete 2-3 pages of scenes with lots of characters around, and only this guy is shadowed! It just ruins the scene!
2- the constant tease of different events we want to see but Oda just continue to tease it until we reach a point that sooo many more interesting stuff are happening that showing it now would be fucking waste of panel.... it happened so many times! Where by the time the pay off comes, we have more interesting stuff we want to see... and those important stuff we want to see will again be delayed for other time when other more important stuff we want to focus on