Will you marry me?

This month, I received two marriage proposals:
The first, in jest from a classmate who’s attached and was just very happy that I arranged an on-campus massage service which was most satisfactory. (I was also called other highly complimentary names by female classmates whose stress was relieved by the massages).
The second, from another classmate who has been more persistent, though for religious reasons I know it will not work out. I laughed it off this time, but if it happens again I will have to give a clear answer. It’s strange as I’ve never been asked this before, until this month.
A question for my readers: If someone you didn’t know very well asked to marry you, how would you react? What do you think is the best way I should react?