User blog comment:LuNa/SBS volume 67/@comment-94.254.85.112-20120911134548/@comment-972068-20120911175537

Luffy doesn't take baths because he doesn't want to.

Zoro doesn't take baths because he's too lazy.

Usopp doesn't take baths because he has I-might-slip-on-soap-and-die disease.

Chopper can't find the cure for I-might-slip-on-soap-and-die disease so he's afraid to take a bath, so Nami and Robin have to make him. They don't call him the pet for nothing.

Franky gets washed, not bathed. There's totally a difference.

Brook doesn't need a bath. He just needs shampoo to keep his hair strong, not that it needs it.