I've only once ever been addressed by someone using the pronoun "otaku."
Taken literally, the word refers to "someone else's house or family," and on rare occasions it is used as the second-person pronoun, "you." The only time it was used to address me was by a police officer in Roppongi, Tokyo, and while it's probably best not to get into the particulars of that sordid episode, it's typical that it was a police officer who used it. In this instance the use of otaku is super-formal, but it still felt weird. At the time I was delighted to hear the word used in its original sense.
Otaku now is mostly taken to mean people with an obsessive interest in something, particularly manga and anime. The nickname seems to have come about because of a feeling that such people are socially withdrawn and never progress beyond calling other people by super-formal pronouns. And while there has been some reclaiming of the name, there is still a negative connotation attached to it.