bywarren, thanks for the advice. I never would have guessed that a man offering to buy me a drink did not have a marriage proposal on his mind. I'm more surprised than I could possibly be. It never would have occurred to me that he could be behaving like boys the world over, whether he is a tourist offering the drink (most likely scenario) or a local (but it does still happen from time to time).
It is not necessary to reject all comers just to prove that you don't have shark food in your hand.