Ragazzaccio is an augmentative and pejorative form of ragazzo (boy).
It literally means "bad boy" or "rascal," often implying someone who is mischievous, rebellious, or a bit wild. In the context of the song, it refers to a young man who is perhaps a bit rough around the edges, but also relatable and perhaps even charming in his imperfections, especially when the singer says "Matto come me" (Crazy like me).
This song paints a picture of a difficult relationship and two very different ways of looking at life. The singer feels insecure around someone who acts tough but is emotionally distant, never offering a "carezza" (caress) and instead crying about their own life without being able to laugh at their troubles.
In contrast, the singer offers a beautiful metaphor: "La vita è come indossare un blu jeans / Più è vissuto e più sarà perfetto" (Life is like wearing blue jeans / The more lived-in it is, the more perfect it will be). He believes that experience, even the tough stuff, makes life richer. He dreams of going back to simpler times, like hanging out in a suburban arcade, and finds comfort in identifying as a "ragazzaccio" (bad boy) who is a little bit "matto" (crazy).