How to speak hip Japanese

When you're unwinding at home and opening up your computer, don't you ever get the urge to study something useful? Or when you're spending a weekend day lazing around at home, that's when you finally feel like doing some self-studying. While in Japan, the urge that always hits me is to practice young people's Japanese. Of course the best practice is speaking with real Japanese students, but I want to get practice even when I'm not chilling with my friends! Though I have yet to find a great resource (well, actually, chatrooms can be useful) I can still help random Japanese-learners stumbling around the web with some basic useful Japanese slang! -ta da!-

Emphasis
- ちょう（超） chyou = very. Use before an adjective, used mostly around Tokyo.
- めっちゃ mecchya = very. This is the same as ちょう except used in the Kansai region of Japan.
- じゃん？ jyan = right? Use this to express your opinion, at the end of a sentence, usually with ん before it. (Like これおいしいんじゃん！)

Onomatopoeia
There's tons of onomatopoeia in Japanese compared to English, and a ton that doesn't represent an audible sound. Here's only a few.
ぎりぎり girigiri = cutting it close, just about.
め/むちゃくちゃ（無茶苦茶）me/muchyakuchya = a total mess
ほっとする hotto suru = be relieved
ぼーとする boo to suru = stare into space, be zoned out

Replies
なるほど/そうか。naruhodo / souka = I see / oh really.
あたりまえ（当たり前）でしょう/じゃん atarimaedeshyou / jyan = Obviously! Duh. (very casual)
まじで？ majide? = really?
ありえない/信じられない arienai / shinjirarenai = No way! / I can't believe it!
なに、それ！nani - sore! = What are you talking about? / What is this?? (pretty casual / rude)
いいなあ/ねえ iinaa / nee = How nice (sorta envious)

Descriptions of People
Maybe it's just me but I think it's fun to inject a little self-deprecation sometimes as a joke in conversation - it's a way to joke around and open up without making fun of everyone but yourself. I think I got this trait from my mom haha. But yeah, here are some words to make fun of yourself or people close to you!
くうきよめない（空気読めない）/KY(けいわい) koukiyomenai / keiwai = can't read the air / clueless
どんかん（鈍感） donkan = thickheaded
あたまがすかすか（頭がすかすか） atama ga sukasuka = airheaded
どじ doji = clumsy
ぶきよう（不器用）bukiyou = awkward (a person)
きまずい（気まずい） ki mazui = awkward (a situation)
ほうこうおんち（方向音痴）houkou onchi = bad at directions (onchi means out of tune)
気もい（気持ち悪い） kimoi / kimochi warui = creepy / disgusting / gross


Text messaging
ｗ = lol
りょうかい（了解） ryoukai = Understood / gotcha

Japanese Laughter
Someone taught this to me once when I was deciding what to use when typing conversation. Not sure how useful it is!
ひひひ hihihi = sorta creepy, perverted laughter
うぷぷ upupu = vulgar laughter
ふふふ fufufu = daring, bold laughter
へへへ hehehe = suspicious, evil laughter. Or bitter laughter.
ははは hahaha = normal laughter