In English, Otaku has come to mean anyone that "is really into" manga or anime. Do not use this word in a Japanese setting, as the connotation is very negative.

You should be very careful around Otaku. Some are extremely sensitive. But don't worry, most don't bite. Here are some general rules to follow. I emphasize general.

1.	Always speak in clear, concise sentences.
2.	Have a copy of The dictionary, so you can decode their reply. Otaku do not like being ignored or asked "what do you mean?", since they think everyone who understands them "is enlightened" (Otaku term for understands the way they talk) and anyone else "does not comprehend reality (Otaku term for Anime/Manga)".
3.	Do not stare. Try to appear taller, but do not wave your arms or legs repeatedly. Do not make any sudden movements.
4.	Do not turn your back. Face the Otaku at all times.
5.	Do not use hand signals. Many Otaku use a code of certain hand signals, for instance if a guy extends his little finger he is referring to his girlfriend. Also certain circles have their own hand signals for identifying their own members. If you make hand signals they are likely to be misinterpreted by the Otaku.