Ussop birthday is on April 1, which is April fools day. This is quite fitting considering his ability to fool people.
In a Manga collaboration with Dragon ball, Luffy was able to ride Goku's cloud which means Luffy had a pure heart.
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.
Sanjis name was originally going to be Naruto until Masashi Kishimoto's manga Naruto was released.