The Japanese writing is suppose to mean "Big Fat Robot". However, my translation skills are extremely rusty, so for all those Nipponphiles out there, please tell me if my hanes and ten tens are where they should be.
Actually, I don't mind if it's horribly wrong, afterall there is a huge market in Japan for meaningless English phrases (go to http://www.engrish.com/ for many hilarious examples). So it should work the other way with equally amusing results. In fact, I remember seeing a GI type wandering around Roppongi with a tshirt written in Japanese kanji, it said "baka gaijin" (idiot foreigner). Not sure if it was an ironic statement on his behalf, or he just thought the letters looked pretty.