Mashi Maro is a chubby rabbit whose name is derived from "marshmallow" because of its seeming resemblence to a slightly bitten one. The story behind the rabbit is that because it is an outcast from society and as a result chooses to act in obsene ways in order to express itself.
This rather strange rabbit has started becoming very trendy. May girls at schools are starting to walk around with Mashi Maro backpacks, pens, pencils, tissue box holders, etc. because it is "cute." It is, however, not contained to just girls, many guys also like Mashi Maro because of its crude humor.
This rather vulgar rabbit has a series of flash movies at http://www.clko.com/. It was created by, well, a company called Clko.
Rant
I may not really comprehend the true nature of why Mashi Maro attracts people to buy its merchandise, but for goodness sakes. Unless you don't care about what people think of what you wear, and psychology knows you do care. If someone saw you with a picture of a fat and rather crudely drawn rabbit with a plunger on its head or a beer bottle to its head. What would they think? That alone is not funny. It's just not funny. To me it looks a little sadistic.