1. I thougth Coby would remined with Luffy but he's not.
2. I thougth Buggy was a ghost, but I found out later that he was not
3. I thougth Luffy was cursed to die because of the skull in the title, I even thougth One Piece was about Luffy figthing off people who wants to kill him or a death-realated situtition
(Yet I did not read Japanese and it's actully a pirate story)
4. I thougth the Strawhats are somewhere in the Grandline between West and North Blue Before that I thougth Whiskey Peak was in Redline. I was like "Wow, why won't the go east?"
5. I thougth Alabasta was on the Redline as the Strawhats are crossing it, I thougth "Wow, how will they get there ship to the other side?"
6. CP9: Shadowy Cult
7. Nico Robin Possessed
8. "Is the Raindeer named Sanji?"
9. Unluckies: Vulture: Mr 13, Otter: Ms. Friday
10. I too thougth the Grandline was not going to be reached untie the end,
11. Because I was confuse with chapter 332 and 337, I was messed up on the Franky and Usopp battle. I thougth Luffy was actully figthing Franky in chapter 332 but it was Usopp, I thougth it was not really Usopp untie I read Stephen's script carefully and read Oceanizer's script. I did not found out my error untie I realized Oceanizer does not have chapter 332 in his site but Stephen's site did. Because of my confusion I thougth Usopp ate the Devil Fruit. I had mixed chapter 332 with chapter 337.
12. When One Piece frist popped up on the Toei site in 1999, I thougth it's just a Toei-invented series like Digimon. At that time I did not know Salior Moon and Dragon Ball Z was based on the Manga. Because I thougth Toei was the authors of these stories and I was like "MMM…that show(One Piece) does not look promising as Digimon. It's no good show. I think it will last 52 episode" But 5 years later, I was reading a Dragon Ball Z manga and I saw the picture of Luffy on the advistisment page, and the series was on American television, I checked the TV Tome site on that series and discovered Arlongpark.com and I was SHOCKED that the series was still running! I thougth it should ended 5 years back. I later dicovered the American One Piece manga in a mall and I saw the name "Eiichiro Oda". That is when I found out the series was manga-based and Oda is still writing the series. Shocking.
13. When I saw Sanji in the opening screen in the anime I saw him spinning around, knocking down his enemies with his feet, judging by how his legs stracthed, I was like " Did that guy ate the Gum Gum Fruit?"
14. When I frist saw Sanji in the group picture in TV Tome site, I thougth that was Helmeppo because Sanji is nearly blurry in that picture.
15. I thougth series would be like Dragon Ball Z where charcters shoots energy and glow with power but none are there (thus disappointing me) But I enjoyed how the story is told and I enjoyed the character flexibility.
Edit: Added more information.
 
I never thought about this… maybe for his Pinocchio's nose 
