You're Zoro's girlfriend, you were bored, and you decided to hang out with Sanji, knowing it would make him jelaous.

You cared of course, but you wanted to see what would happen if you suceeded.

While you were talking with Sanji you noticed Zoro staring in the corner of your eye.

Later that night, you were doing whatever you would usually do, when you felt a strong hand on your waist...Zoro's.

What were you doing with him?

he asked in a stern tone.