This is the point where I should probably differentiate between the Italian language, and Roman slang…
Italy is divided into 20 regions: each region has its own dialect and slang. This is apart from Sardinian (and Sicilian kind of), which is practically its own language. An Italian’s accent, cadence, and slang are all a dead give away to where he or she is from. Romans are no exception: they have a very distinct accent and vocabulary. Romanaccio, or Roman slang, is mostly heard among teenagers (ugh teenagers), but certain words and sounds are definitely used by Romans of all ages. There are many websites that sum up the ‘rules’ of Roman slang, my personal favorite is, Er Romanaccio.
Ammazza, a Roman word used by all Romans, basically means, ‘wow!’ It is used when exclaiming over anything. It comes from the word meaning to kill, or ammazzare. Ammazzare comes from the Italian noun, mazza, or a bat, a club. I suppose the shock that comes with killing, is what lead to the exclamation, ammazza! You can use this exclamation in reference to practically anything. It is not a curse word in any way, and like I said, people of all ages use it quite often.
‘Ammazza che fila!’ – ‘Woah! What a [long] line!’
‘Ammazza, che cena!’ – Wow! What a dinner!’