Thanks to Vampire Apple for mentioning Ace! I love how Zoro reacts differently from everybody else when it comes to Luffy. I take it as a result of their deep understanding of each other. This is set right after Ace meets Luffy and his crew during the Alabasta arc, in which Zoro knew Luffy would decline Ace's offer.
Ace didn't bother to glance back at the burning marine ships he left in his wake as he landed on his boat. A bemused smile found its way along Ace's features as the Devil Fruit user thought of his little brother and his crew.
The quickest way to evaluate the future of a pirate ship was through the first mate, the being who stood between the captain and the crew. No matter how powerful the captain was, if the first mate showed doubt, the crew mates would in turn, mimic the distrust and the crew would crumble. If the first mate did not waver, it was only a matter of time before the other crew mates trusted their captain with the same intensity.
Though his brother hadn't had the time to introduce his crew mates individually, Ace had found the first mate quite easily.
When Ace offered Luffy to join White Beard's crew, most had gasped or stiffened in their captain's defense.
Only one had laughed.