There is only one thing to be said about Italian slang: There is no Italian slang!!
Italian speakers have nothing similar to the French verlan and trying to find rules or build dictionaries on Italian slang language won´t lead anywhere. Young Italian speakers speak a mix of dialectal expressions and geographical-related slang words. Those groups are really small, though. Even between teens from the same region but from different cities there could be misunderstandings while talking!
Nonetheless it´s possible to summarize some general trends of the Italian multiple slangs:
1. All of them stick to specific vocabularies, which are: youth entertainment, police nicknames, people categories, sex and school.
2. The regional and dialectal component is very strong and defines the local slang.
3. The first two rules are true for North and Central Italy but cannot be applied in the South because on those regions dialects are still thick on the ground.
Going back to the categories listed upon I would like, now, to present you some examples for each of them. I tried to select the most common, current and widespread slang words used in Italy. If you have any other example, feel free to send your word contributions posting them on the comment section.
Specific Slang Vocabulary 1: Youth Entertainment
Even if ciao is one of the most widespread words in the world some Italians like to greet friends saying bella or bella lì. Going out is also a good occasion to use slang words, which are related to the most common youth activities, like for example…
To drink Booze: Benza
To get drunk: caricarla grossa
To be drunk: essere fraido, essere fuori come un balcone
To puke: arcaccia’
To smoke cigarettes: fumare una siga, una cicca, una paglia, ecc…
To smoke joints: farsi una canna, un cannone, fumare la gangia,la maria, l’erba, ecc…
To be stoned after smoking a joint: essere in botta, avere una briscola, avere una tavola, ecc…
Specific Slang Vocabulary 2: Police Nicknames
There is a lot of nicknames used to talk about the police, the most commonly known are: Pula, pulotti, caramba, sbirro and piedipiatti.
Specific Slang Vocabulary 3: People Categories
How would you say boyfriend or girlfriend? Italians would say: frego/a, tipo/a, ecc…
How would you call a beautiful chick or guy? Italians would use: fica/o, figa/o, bona/o
Please note the coming words are impolite and often imply a negative evaluation of the subject!
How would you define an ugly girl? Cozza, cesso
And a chubby one? Buzzicona
Did you know that Italians have a nick for the South Italians? They are called terroni.
Specific Slang Vocabulary 4: Sex
Condoms: goldone, coso
To hit on a girl: baccagliare, provarci, inciuciare
Don´t be so full of yourself (it´s not the very exact translation, though): Non tirartela!
Boobs: Airbag, davanzale, tette
To screw or to fuck: chiavare, scopare, fottere, bombare, infrattarsi
Specific slang Vocabulary 5: School
At school you can…
…be caught copying from your friend´s test, which can be translate with essere cioccato
…fail, which would be cannare
..skip a class which can be translate with thousands of verbs, like: fare sega, fare salina, bigiare, ecc…
…be called lecchino or leccaculo if you are an ass-kisser with your teachers
or you can be called boccia or boccino if you are in your first year at school.