Boicotta comes from the verb "boicottare," meaning "to boycott." It's an interesting and somewhat unexpected word to find in a song about a tumultuous relationship, making it stand out.
In the lyrics, "il mondo ci boicotta" (the world boycotts us) suggests an external force working against the lovers, adding a layer of dramatic conflict to their already strained relationship. It elevates the personal struggle to a more universal, almost rebellious, level.
The title does the work here. Tristan and Isolde drink a love potion by mistake and spend the rest of the legend loving each other to death, and Kid Yugi puts that at the centre of a breakup he keeps re-describing: "Il nostro amore che ci uccide alla Tristano e Isotta" (our love that kills us, Tristan and Isolde style). He even keeps the armour. "Solo il tuo sguardo mi ferisce e penetra la cotta" (just your gaze wounds me and pierces my chainmail) is a knight taking a hit, except the weapon is somebody looking at him.
What makes it more than a costume is that he moves the blame halfway through. The first chorus opens "Come ti sei ridotta" (look what you've been reduced to); the second opens "Come ti ho ridotta dando a te la colpa" (look what I reduced you to, putting the blame on you). Same melody, one pronoun different, and the whole song turns on it. The second verse is a list of things he suspects about himself, read out flat: "Che sono un buono a nulla, che mi sento un perdente" (that I'm good for nothing, that I feel like a loser). He is hard on himself and not convinced that counts for anything, which is why the closing line lands the way it does: "Ti chiedo scusa ma non serve" (I'm asking your forgiveness but it's no use).