I usually just call myself a weeb self-depreciatingly. Just like I say "Chinese Cartoons" or "Animoo".
In Japan you wouldn't really call yourself an otaku, rather avoiding it and only perhaps admitting it in the company of other fellow nerds. There's also the whole kimo-ota stereotype, that you'd want to dodge.
In fact being called otaku by non-otaku can be kinda jarring depending on context. (Thus we have roundabout expressions like "Akiba-kei" meaning Akiba-style or Akihabara-style being a bit softer, althought I've only ever heard the expression on this TV program where they were interviewing nerds).
But calling yourself otaku, especially when in English, sounds a bit like you're a try-hard. And from the Japanese view it's kinda wierd to want to self-inflict with label that, unfortunately, still has many negative stereotypes associated to it. That being said Otaku culture is coming in to the mainstream more and more much thanks to our Vocaloids and Keions which have garnered mainstream appeal.