I thought this was funny sound it on some Blog, a Blog that was not in english. I think that this is the T-Shirt equivilant of getting a tattoo with Japanese letters that you really have no idea what it says. So unless I am missing something this Shirt makes no sense.
So yeah I think they might have been trying to say something like "I'm Just Blogging" or " I am Blogger" or "I'm Just a Blogger" but I guess you could wear it to confuse people. Seems like a good use.