"You're a boy" is an English equivalent of the Italian phrase Sei un ragazzo. The second person informal singular present indicative with masculine singular cardinal number/indefinite article and noun also translate into English as "You're one boy (boyfriend, dude, kid, young man)" according to context. The pronunciation will be "SEH-ee oon ra-GAT-tso" in Italian.
Chi sei? in Italian is "Who are you?" in English.
Sei bravo! in Italian means "You're good" in English.
Sei bella! in Italian means "You're beautiful!" in English.
"Six" in English is sei in Italian.
sei li?
Perché sei arrabbiato? in Italian means "Why are you angry?" in English.
Tigrotta sei! in Italian means "You're a little tiger!" in English.
"You are special!" in English is Sei speciale! in Italian.
"You are horny!" in English is Sei arrapato! in Italian.
"Are you safe?" in English is Sei salvo? in Italian.
"You're in charge!" in English is Sei in carica! or Sei responsabile per...! in Italian.
Sei un cavallo! in Italian means "You're a horse!" in English.