Okay, given the animosity that seems to be building up with yet another argument of what is an otaku, here I go.
It seems more and more out west (outside E Asia), otaku is becoming less and less otaku and more "I watch anime." Personally, I don't like the "all-inclusive" move; it feels just like in elementary school when everyone would get some award just to make everyone feel good. What's the point of using the word otaku if it just means you watch anime? Why not just call yourself anime watcher (like I call myself)?
For me, otaku generically refers to someone with an almost unhealthy (okay, just plain unhealthy) obsession with the anime culture and subculture, specifically dependent on the adjective in front (like car otaku). Anime culture, unbeknowngst to many outside Japan, is not just anime but includes manga, doujin, games, Akihabara, etc. Also, to just watch anime but not know anything (see below) definitely does not pass as an otaku. And lastly, otaku should not be a label you have to tag on yourself. People should be able to tell if you are an otaku; you should not need to shout it out. Just like if you're telling everyone that you're smart, or you're a crazy Trekkie, you're probably not and just want the label for yourself.
Now, for common things I hear from wannabe and self-proclaimed otaku that blatantly say "I'm not an otaku" to me, or just bother me.
1) I'm an otaku. I hate old anime (usually pre-Eva). I ask, "Have you seen any?" They say, "No."
My thoughts: If a muscle car fanatic said "I hate all 1960's cars and never seen one," what would you say? Can you call yourself even an anime fan if you won't watch a huge segment of anime?
2) Doujin is hentai
My thoughts: You have no right to complain about people saying anime is hentai. Or call yourself an otaku for not knowing what doujin is.
3) I'm an otaku. My favorite shows are Kanon, Shuffle, KGNE, etc. I don't know they are from hgames.
My thoughts: I'm sorry, but an otaku not bothering to figure out anything about their favorite shows? Real otaku know those are from hgames WITHOUT ever seeing them, and you're telling me that you don't know the most basic fact about your favorite show?! And this applies to anime from manga, games, novels, etc.
4) I'm an otaku and Naruto and Bleach are for adults.
My thoughts: The Japanese created this for kids. What, after twisting the word otaku to make you happy, now you twist the show's target audience? Or are you so ignorant an otaku to not know that?
5) I'm an otaku. I only watch shounen/ecchi/mecha/etc. I won't watch shoujo/slice o'life/drama/etc.
My thoughts: The genres might be changed up, but for the most part you know the ones I put in are the most common. Basically, like the old anime thing, you ain't an otaku when you won't try a whole section of anime.
6) What's Comiket?
My thoughts: Just no. I don't care whatever else you say or do. You aren't an otaku.
7) I'm an otaku. I'm an otakukin.
My thoughts: Let me point you towards a psychiatrist. In your case, I'll call you an otaku, just to prevent you from becoming more unbalanced.
8) I watch a ton of anime so I'm an otaku.
My thoughts: I watched a ton of anime and I don't consider myself an otaku. If that's the case, why don't we just say anyone who's watched anime for x number of years is an otaku?
9) I spend all my paycheck on anime so I'm an otaku
My thoughts: No, you just have no money management skills. Since when was otaku defined by money?
10) I'm an otaku. What's Touhou?
My response:
Basically as you can see, a lot of the points boil down to a lack of curiosity and knowledge about anime and the culture. That's the biggest sticking point for me. I don't care if you've seen 10,000 anime and been watching for 30 years. If your favorite show is Kanon and you don't know anything about it outside the anime, you're not an otaku. If you just plain avoid certain sections of anime completely, you're not an otaku.
And if you blanket label one media (see doujin), don't bitch about people doing that with anime.