The name is a combination of the two grandsons of Prophet Muhammad, Hassan and Hussein.
Hassan literally means "good".
Hussain means Younger Hassan.
Stranger: Sorry, come again---Ha?
Me: Just call me Haz.
You can pretty much tell a "hasnain" from the rest of the crowd. He is the person that makes your head turn.
Hasnains are also very intelligent. They are good people to sit next to during exams.