I really don't know. Being anime fan is fine, I love anime but in Japan being caller an Otaku has... well as you said, negative connotations. It's not as plain a translation as people think.
And most people who call themselves Otaku are really 'weeaboos', meaning foreigners who think they know what an Otaku and Japanese culture is like and really don't.
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Personally I think being a weeaboo is just as bad as being an otaku, because being a weeaboo is pretty much showcasing ignorance for the Japanese culture.
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I'm pretty much on that, if you are calling yourself an Otaku you're... really using the term wrong. Japanese people would cringe at you