In a Manga collaboration with Dragon ball, Luffy was able to ride Goku's cloud which means Luffy had a pure heart.
Ussop birthday is on April 1, which is April fools day. This is quite fitting considering his ability to fool people.
Whitebeard (Edward Newgate), unlike other devil fruit users doesn't name his attacks.
The reason why Zoro dislikes Sanji is because he treats women differently than he treats men, and ever since Kuina complained about being a girl, Zoro is set on the idea that gender should not decide how you treat a person.
As Zoro practised Swordplay when he was young, he would get his ears pierced, whenever he mastered a sword style. That's why he has three earrings, one for each sword style.