Just like the title implies, words and phrases that won't appear in your dictionary but have deep meaning and frequent use in casual conversation.
Just a few I've learned.
Koukii Yomenai, liturally translates "the air (atmosphere) cannot read". K Y for short. It's used when encountering someone who has a different conversation going on than the rest of the group. Like saying "you don't know what you're talking about".
Chinpun Kanpun, means: I have no idea. Better than saying wakarimasen all the time.
Kuru Kuru Paa, like saying someone is crazy........or dumb. Comes across better than calling someone baka, but it's still rather insulting.
Chou, this one I like and use often in speech. Means "very", but not really. In english we sometimes say something is "effin" good, delicious, etc. This is like your Japanese effin.
Yabai, means "that's bad", but couple that with chou and you get chou yabai, meaning "that's effin delicious".
Mecha, another form of very, used casually between friends. When I'm asked "genki desuka" I often reply "mecha genki daiyo".
There's also regional slangs, namely the ones from Osaka that are commonplace for people from Osaka but unusual to people from other parts of the country.
Maidou, a greeting when entering a store. Instead of "irashai mase" Osaka-jin tend to greet their customers with this.
Okini, means "thanks".
Nande Yannen, means "you're kidding" or "no effin way". Usually couple this phrase with a small love tap to the listeners head.
Anyone else know any good slangs? Please reply them here. Also, if you could let's keep it to Romaji so everyone can read them.