You won't learn this in your Japanese class, not if you have the kind of stuffy teacher who is mortified by the prospect of her charges speaking improper Japanese like I did. My six months of Japanese lessons never prepared me for the way people actually spoke. I'm not talking about the dialects, the hôgen, about which I sometimes write. No, what I'm getting at is the colloquial Japanese spoken by young Japanese.
Teaching young women at two different universities, I am exposed to this fairly new kind of speaking on a daily basis. The classes I am in charge of at one university are called "Supisuki" by the students. That real title of the class is "Speaking Skills" (スピーキングスキル → スピスキ). I once taught a Reading Skills class that the kids called "ライスキ" (ライティングスキル → ライスキ).
It doesn't stop with class names, of course. Nearly everything can be abbreviated--nouns, adjectives, verbs. The above word uzai is a corruption of uzattai, an adjective meaning nitpicky, troublesome, a hassle, persisitent, and confusing.
Gurotesuku (grotesque) → GURO (グロ！)
Makudonarudo (McDonalds) → Makku (マック)
Suma-tofon (Smart Phone) → Sumaho (スマホ)
★ Incidentally, I'm trying to get young people to say kashiden (カシ電) as in kashikoi keitai denwa (clever mobile phone). There have been precious few converts.
Kimochi warui (uncomfortable, disgusting) → kimoi (キモイ)
★ The slang form, like guroi, sounds more disgusting than the original.
Nomi hôdai (all you can drink) → Nomiho (のみほ)
Tabe hôdai (all you can eat) → Tabeho (たべほ)
Mabushii (bright, as in blindingly so) → Mabui (まぶい)
Keitai denwa (mobile phone, cellular phone) → Keitai (携帯)
Riaru ga jûjitsu shiteiru yosu (The sense that "real life", namely that life when not working or going to school, is fulfilling. Used among otaku and NEETs) → Riajû (リア充)
Kashisu Orenji (Casis Orange cocktail popular with young women) → Kashiore (カシオレ)
Gûguru de kensaku suru (Google something) → Guguru (ググる)
Kurisuto Kyôgaku (Christianity Studies class) → Kurikyô (クリ教)
Chûtohanpa ja nai (Not half arsed = great) → Hanpa janai → Hanpa ne~ → Pane~ (ぱねぇ)
Muzukashii (difficult, hard) → Muzui (むずい)
Mendôkusai (troublesome, meddlesome, a hassle) → Mendoi (めんどい)