One Piece Chapter 30, page 8-10: GREAT!!!

Jango points forward and commands his empowered crew, "GO..! KILL THOSE PESTS!!" The pirates charge forward, screaming wildly. Seeing the danger, Zoro turns to Nami and Usopp and orders, "YOU TWO HURRY AND GO UP THE SLOPE! WE'LL TAKE CARE OF THIS..." But as Zoro prepares to fight, he notices Luffy standing completely still with a bizarre, intense expression. Zoro calls out, "HEY! LUFFY! LUFFY!?

Luffy throws his arms in the air and lets out an incredibly loud roar: "YEAAAAAAAAAHHHHH!!!" He has accidentally been hypnotized by Jango's pendulum as well! Zoro, Nami, and Usopp are completely flabbergasted, with Zoro screaming, "YOU GOT HYPNOTIZED TOO?!?" Jango is also taken aback, sweating as he thinks, "EH!? HE'S NOT YOUR AVERAGE IDIOT... GOT HYPNOTIZED SO EASILY..." The hypnotized Luffy charges forward alongside the pirates, roaring.

Fueled by the hypnotic rage, Luffy unleashes a devastating attack. He winds up his rubber arms and launches a rapid-fire barrage of punches, shouting, "GOMU GOMU... GATLING GUN!!!" A storm of fists rains down on the charging Black Cat Pirates, completely overwhelming them.