Okay, my name may be Miyako, but I'm not Japanese and can only speak a miniscule amount of the language so I may or may not be right. If you read as many fanfics as I do you kind of memorize them. Below are the some of the words that fans may choose to use in their anime fanfics.
Update (5-10-01): I added kawaii (can't believe I forgot that), kuro, hikari, iinazuke, tomodachi and corrected gou. By the way, Jinzouningen *does* mean man-made men (or artificial humans). What do you think androids are?
Update (6-26-01): I corrected a mispelling in 'gomen nasai' and konban-wa. I added tenshi, shojo ai, and yuri.
Update (9-9-01): I added onegai, hime, neo, ningen, and arigatou gozaimazu.
Update (9-25-01): I fixed one phrase (it's *ohayo* gozaimazu, not arigatou gozaimazu) and added sofubo, futaoya, gaki, bozu, and bishojo.
Update (3-17-02): Added koibito, owari (I accidentally left these two out), minikui, baishunfu, omae, & hisama courtesy of Q-TIP. Omake & koi are my additions.
Update (11-9-02): I added koishii, hana, sumimasen, shine, shoyuu, seme, and uke. Iíve seen a lot more, but canít remember all of them. Next time Iím going to have to write them down.
Update (5-29-05): Did some cleaning up format-wise and re-added "arigatou gozaimasu" because it is grammatically correct to use this.
-chan: a sign of affection for small children, close friends (generally used by girls), and boyfriend/girlfriend or husband/wife, added after someone's name or nickname
-gou: the counter for general objects
-kun: for male classmates and male friends
-sai: the counter for age
-sama: used for respect, beyond "-san" (kings, queens, emperors, religious leaders, etc.)
-san: Mr./Miss/Ms./Mrs. -- it's added on the end of a name to show respect. It can also be added after the name of a job title if you don't know the person's name. Example: Secretary-san, Officer-san.
Bakayaro: idiot (a level beyond a regular idiot)
Arigatou: thank you
Sweatdrops: Used for when someone makes a *very* stupid comment. Can be used for exasperation as well as nervousness.
Face vaulting: If something is beyond stupid, this is used instead of a sweatdrop. It's also used if a character says/does something unexpected for a situation.
Nose bleeds: Used generally for men when they are embarrassed by a sexual topic or has seen something related to sex that embarrasses them.
The magical appearance of weapons: This is just as it says. Can be anything from ChiChi's heavy artillery to Misty Waterflower's mallet. Heero pulls a gun from no where too. They call his place 'Spandex Space'. Where do they really come from? No one knows.
The big head effect: Applies to Misty Waterflower of Pokémon and Bulma Briefs of Dragon Ball here. Used for intimidation and anger.
Glomping: When someone attatches themself to another person in affection.
Pocky: A Japanese snack food. It's basically just a wafer stick dipped in strawberry, chocolate, etc. It's very popular (and good!) and lots of people use it in their stories. You can buy it online at http://www.japanesesnacks.com.
The way Japanese phrase sentences are way different from the English language. They usually put proper nouns first and adjectives directly after them and verbs always go at the end. They also put their last names first. That's all I can tell you now, but I hope to know more.
Am I wrong about something? Do you want to add more? Then e-mail me (or leave a review) and I'll update the dictionary!