me too.better called him marimo!even i dunno what its mean.

i heard its because "bushido" means "way of the samurai" which is likely what zorro does

I think 'bushido' means 'warrior'.... Mr. Oda said that...

Bushido means "Way of the Warrior Knight. It is a Japanese word which is used to describe a uniquely Japanese code of conduct and a way of the samurai life. Basically, it's all about being chivalrous and "loyal unto death". Zoro, though he is not a Samurai, portrays, in a way, Bushido; the way of the warrior. That's why Vivi calls him Mr. Bushido. It is a part of who he is. Just as she calls Usopp Mr. Long-nose (though not in quite the same way).

Because it is a fitting nickname. Lol. Bushido being a warrior, basically, definitely applies to Zoro. XD

i think that bushido means warrior samurai plus zoro is one