Way too hard to pick the funniest moment. I'd have to rewatch the series again (which doesn't sound too bad)
I got a kick out of the short scene in the Arlong arc, when Luffy was mesmerized by a pinwheel on that guys hat, despite being in a precarious situation.
Another one that made my side hurt was when Luffy woke up after that huge feast to find a bunch of villagers, who served him earlier, slaughtered by Zoro. Oblivious to what's going on, since Luffy was in a deep slumber, he goes after Zoro. The ensuing fight was hillarious.
Usopp has many funny scenes as well, most of which are scenes of Usopp chickening out after some smack talk.
