Sweet 16 is for the 16th birthday, which for girls is important because it symbolizes the becoming of a woman. For guys it's just another birthday, so they could give a shit less about it.
Bday girl: omg i'm turning 16 omg! This is going to be the bestest bday eva! I'm going to get so much, most likely a CAR! Best of all i'm going to be a woman!!
Another girl: omg i'm sooo happy for you omg! I can't wait untill i turn 16!!
Guy: Dude your turning 16 on tuesday. So it's going to be your sweet 16, you excited?
Bday guy: Psshh and i care because? Dude it's just another fucking birthday, nothing special.