One Piece Chapter 24, page 18: Things That You Can't Lie About

Usopp screams with absolute pride and fury, "I'M PROUD THAT MY DAD WAS A PIRATE!!! I'M PROUD THAT HE WAS A BRAVE WARRIOR OF THE SEA!" He glares down at Clahador, declaring, "YOU'RE RIGHT THAT I LIKE TO LIE, BUT I'M PROUD OF HAVING A PIRATE'S BLOOD IN ME!! I DON'T HAVE TO PRETEND THAT I'M NOT!!! I AM THE SON OF A PIRATE!!!" Luffy, Zoro, and Nami watch him. Hearing Usopp's words, Luffy's eyes widen in realization as he says, "OH YEAH!! THAT GUY..!! NOW I REMEMBER...!!"