One Piece 235
I already knew Usopp and Luffy fought (I mean, it's in the full version of the opening). And it was mostly clear once they mentioned that the Merry couldn't be repaired to Luffy and Nami why animosity would start to form. I think the build up was mostly good, largely due to Usopp's attachment to the Merry and a refusal to let go. The character had started to realize what he was not capable of (compared to the others) and blamed himself for the lost money. Even after Luffy straight-up tells him the ship can't be repaired and that money isn't the problem, his self-blame in addition to refusal to lose the merry culminates where Usopp isn't totally rational at the moment.
I think this is the first time we truly see a confident Usopp, who believes he can beat Luffy to get the Merry back. He's certainly shown 'bravery' in the past as he sometimes gets a momentary burst of courage to do something notable, but I think this is the most determined we've seen him, despite acting a bit irrationally.
(... unless I'm forgetting a key Usopp moment before this)